With no end in sight to hostilities, Sky News has mapped the assaults on both sides - and the military assets at play in the region.
A regional conflict
The US began Operation Epic Fury with a series of strikes on Saturday morning, killing Ayatollah Ali Khamenei in his Tehran compound.
Israel joined the assault, killing dozens of top Iranian military officials in aerial strikes.
Iran retaliated by launching drones and missiles targeting Israel, the UAE, Bahrain, Jordan, Oman and Qatar.
Three American service members were killed in a strike on Kuwait, while an RAF base in Cyprus was also targeted in a drone strike.
How far can Iran strike?
Iran's drone attack on RAF Akrotiri in Cyprus was a demonstration of its capabilities.
Its longest-range missile, the Sajjil, has a similar maximum range of up to 2,000km (1,240 miles), according to the International Institute for Strategic Studies, a defence thinktank.
That's far enough to hit Moscow or Athens, though still well short of giving Iran the ability to strike the UK.
The UK's base in Cyprus is well within range of not only the Sajjil, but also Iran's Ghadr and Emad-1 missiles.
Fighter jets and airbases
Sky News Data and Forensics team has plotted US and UK air bases in the Middle East and Europe that can be used to launch attacks on Iran.
Over the past few weeks, US and RAF aircraft have flown to and from the Middle East, with a significant build-up at the bases.
Aircraft such as F22 fighter jets, C-17 military transport planes and KC-135 tankers are among the assets deployed by the US.
Diego Garcia is one of the airbases which has seen an increase in activity.
The site has been in the headlines over recent months, with Donald Trump criticising the UK's plans to cede control of the Chagos Islands to Mauritius.
The Iran conflict has highlighted the strategic importance of the joint US-UK military base, with Sir Keir Starmer refusing permission for it to be used by the US to launch strikes on Tehran.
Satellite imagery captured over the base on Sunday morning shows at least 14 planes stationed next to the runway, including six F-16 fighter jets and two P-8 Poseidon maritime spy planes.
The rest are transport aircraft, including a C-5 Galaxy and three KC-135 Stratotankers, analysts at Jane's Defence Weekly told Sky News.
The C-5 is the largest transport aircraft in the US arsenal, capable of transporting military vehicles and even fighter jets.
Flight tracking data shows that the C-5 belongs to the US military and arrived from South Korea on Saturday. A KC-135 Stratotanker was also seen en route to the base the same day.
As of Monday afternoon, flight tracking data shows a second US military C-5 was en route to Diego Garcia from the joint US-South Korean Osan Air Base.
Analysts at Jane's Defence Weekly told Sky News that the UK does not operate any of the aircraft models visible in the satellite imagery, except for the P-8 Poseidon.
Naval assets
Sky News Data and Forensics team has been tracking US military ships in the Middle East.
At least three US military ships are reported to be in the Persian Gulf, and 12 around the Middle East and Mediterranean.
The aircraft carrier USS Abraham Lincoln was seen under 200km (124 miles) from the coast of Oman on 25 February.
The Lincoln is one of the world's largest military ships and can carry different types of aircraft including F-35 Lightning II fighter jets.
The nuclear-powered carrier was visible on satellite imagery.
It was accompanied by an unknown ship measuring over 200 metres and was potentially used for replenishing or drills.
The largest aircraft carrier in the US naval fleet, the USS Gerald R Ford, was last seen on satellite imagery on 27 February in the Mediterranean Sea, just under 400km (248 miles) from the coast of Cyprus.
It was reportedly travelling with three US destroyers, capable of carrying more than 6,000 personnel in total.
Sky News has also tracked six Iranian ships using data from TankerTrackers, situated by Qeshm island in the strait of Hormuz.
They were last seen on satellite imagery on 28 February.
These ships have been in the area for more than two weeks. One of these is the Islamic Revolutionary Guard Corps' Iris Shahid Bagheri, Iran's first drone-carrier warship.
Frequently seen in the Strait of Hormuz, the ship can deploy around 60 drones, in addition to helicopters.
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Maps created by data journalist Alicja Hagopian, digital investigations journalist Ben van der Merwe, junior OSINT producer Freya Gibson, OSINT producer Lydia Morrish and junior digital investigations journalist Sophia Massam. Copy editing and production by Adam Parris-Long, assistant editor
The Data x Forensics team is a multi-skilled unit dedicated to providing transparent journalism from Sky News. We gather, analyse and visualise data to tell data-driven stories. We combine traditional reporting skills with advanced analysis of satellite images, social media and other open source information. Through multimedia storytelling we aim to better explain the world while also showing how our journalism is done
It is only a few days since Iranian and American diplomats sat down in Geneva to discuss the details of a possible nuclear agreement. Now, the Ayatollah is dead, along with dozens of Iranian leaders, while Iranian missiles are fired at an array of countries across this region. Life is coming at us fast.
What is clear is that Iran has three ambitions, and it needs to do them all at the same time.
Firstly, it needs to find itself a new leader, and a layer of people to go alongside him. That search is, according to those within the country, being fast-tracked to such an extent that a new Ayatollah could be named within the week, allowing a focal point to be re-established.
Secondly, Iran is keen to tell the world that it is the victim here - that it had negotiated in good faith and was tricked by its two greatest enemies, America and Israel.
Certainly it is hard to see how, under the terms of international law, this war could be described as legal. Israel was not seemingly facing an imminent threat from Iran and the United Nations Security Council did not authorise this attack. What's more, President Trump did not attempt to even secure the support of Congress.
Of course, both Israel and America are well aware that the Security Council would not have supported this action - a veto from Russia and probably China was inevitable. They are also aware that the standing of the UN has rarely been lower, with Donald Trump (to an extent) and Benjamin Netanyahu (massively, repeatedly) criticising the UN as a busted flush.
Iran's third ambition, and the most overt one right now, is to turn this war into a regional conflict. Eight months ago, the 12-day war largely involved Israel and Iran trading missile bombardments. This time, it's very different.
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Now, Iran has embroiled gulf nations, attacking them repeatedly. Debris landed by a Saudi oil refinery, missiles were in the air above Jordan. Hezbollah, loyal to Khamenei, launched a rocket attack against Israel from southern Lebanon, triggering a furious response that has killed more than 30.
The Strait of Hormuz has been rendered almost unusable, Qatar has stopped selling natural gas, and the price of oil has sharply increased. Even a British air base in Cyprus has been attacked.
The ripples of this conflict are spreading, which is exactly what Iran wants - a war that disrupts life for a huge swathe of the world, tests alliances and leads countries to push for an early end.
But there may be another tactic here from Iran. If the remnants of the regime, notably what's left of the leadership of the Revolutionary Guard, think their grip is being prised from the country, they may be tempted to launch one final massive salvo against the many countries they see as their enemies.
It is a fearsome, intimidating prospect. Is it feasible? Perhaps - it has certainly been talked about for years. But would they actually do it, or this simply another carefully curated piece, a dreadful threat that the Iranians are quite happy to allow to live in the ether?
If Iran were to change path - whether to become more authoritarian, more moderate, or even to change to a wholly new form of government - the knock-on impacts would be enormous. It is a country of central importance in every way. And this is a difficult, precarious time in a region that is loaded with long-standing volatility.
"Tell me how this ends" was the statement posed by General Petraeus when confronted by the quagmire of Iraq, and it remains a very pertinent question, not least today in the Middle East.
We simply don't know the answer and it's not clear that either America or Israel are asking the question. The lessons of the past are that it's easy to start a war but hard to rebuild afterwards. Now, even as the Middle East reverberates to the chorus of air-raid sirens, the future is being shaped. But nobody quite knows how.
Sky News understands UK officials are working on plans for potential routes for the evacuation of tens of thousands, should airspace in the Gulf remain off-limits.
British Foreign Secretary Yvette Cooper told Sky News on Monday morning that the UK government is "working on every possible option" and teams have been deployed to the Gulf countries to help Britons there.
"Of course, we want people to get safely home as swiftly as possible," she told Mornings with Ridge and Frost.
As Iran retaliates to US and Israel strikes with counterattacks on military and other targets across the Gulf, major airports have been forced to close for a second day, including the world's busiest international hub in Dubai.
It has sent shockwaves and the most severe business disruption through the Gulf since the COVID-19 pandemic.
Ms Cooper said about 300,000 British citizens are in the region, including residents, tourists, and those in transit.
By Monday morning, 102,000 - most of them in the United Arab Emirates (UAE) - have registered their presence in the Middle East on an online government platform launched after the conflict began on Saturday.
The majority have been moved to hotels, in what is one of the biggest consular cases the Foreign Office has had to deal with in recent years.
On Sunday evening, Prime Minister Sir Keir Starmer said: "Over the last two days Iran has launched sustained attacks across the region at countries who did not attack them.
"They've hit airports and hotels where British citizens are staying.
"This is clearly a dangerous situation."
British nationals are currently being advised to stay where they are, follow the instructions of local authorities and monitor the Foreign Office's travel advice.
On Sunday, the PM also said he would permit the US to use British bases for defensive strikes against Iran. The Liberal Democrats warned against a "slippery slope" that could see the US "drag Britain into another prolonged war in the Middle East".
But Ms Cooper insisted allowing the US use of UK bases is "about the defence of our partners in the Gulf" and of countries "where we have so many British citizens and interests".
"We continue to believe that we want to seek a negotiated solution, a diplomatic process," she added.
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Thousands of flights cancelled
More than 3,400 flights were cancelled on Sunday across seven airports in the Middle East, according to flight tracker Flightradar24.
Disruption has hit Doha in Qatar - which handled 54 million passengers last year - as well as Bahrain, Israel, Jordan, Kuwait, UAE and Saudi Arabia.
And with airports in Qatar and the UAE often used for connecting flights, the disruption could hamper onward travel plans for passengers across the globe.
Even further afield in Bali, more than 1,600 tourists were stranded after five flights to the Middle East were cancelled or postponed at I Gusti Ngurah Rai International Airport, officials said.
Departures and arrival boards at Heathrow, Gatwick, and Manchester airports listed multiple flights serving destinations across seven countries as cancelled.
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Aviation analyst Cirium estimates that 90,000 passengers per day fly with Emirates, Etihad, and Qatar Airways at Dubai, Abu Dhabi, and Doha alone.
'Drones were exploding in the sky above us'
Jo Hummel, 43, and her husband Chris Jenkins, 46, were travelling back from Thailand with their two children, Ivy, 17, and Kit, 12, when their connecting flight from Doha to London was cancelled.
Ms Hummel, from the Isle of Wight, said: "We touched down into Qatar and people were opening up their phones and there was a national alert coming through in Arabic. We realised something was going on.
"We were transferring in Doha to London and everything was getting cancelled."
She continued: "Qatar [Airways] staff came and offered us a hotel room, at first we were going to stay at the airport, but now we are 20 minutes away in a hotel organised by the airline.
"I had to get them out of bed this morning because drones were exploding in the sky above us and we have big windows. It's quite frightening.
"As a mother, I'm scared out of my wits and trying to keep calm, but also be organised.
"I don't think anything will leave until it's safe."
In new travel advice issued overnight, the Foreign Office advised UK nationals against all but essential travel to Bahrain, Israel, Palestine, Qatar and the United Arab Emirates.
In a statement, the department said: "British nationals in Bahrain, Israel, Palestine, Qatar and United Arab Emirates can register their presence to receive direct updates from the FCDO on the situation in the Middle East.
"You should continue to follow travel advice and the advice of the local authorities."
Henry Harteveldt, an analyst with Atmosphere Research Group, said: "For travellers, there's no way to sugarcoat this."
They should "prepare for delays or cancellations for the next few days as these attacks evolve and hopefully end", he added.
The strikes on Iran on Saturday led to the death of Iran's Supreme Leader, Ali Khamenei, Iranian state TV eventually confirmed.
In the retaliatory strikes that followed, two UAE airports reported incidents as the government condemned a "blatant attack involving Iranian ballistic missiles".
Officials said four people were injured at Dubai International Airport, while one was killed and seven others were injured in a drone strike at Zayed International Airport in Abu Dhabi.
Also in Dubai, an explosion and subsequent fire occurred near the entrance to the Fairmont The Palm hotel.
Airlines that typically traverse the region may choose to reroute flights, leading to longer travel times, rising fuel costs, and eventually higher ticket prices.
It remains unclear how long disruption will continue, with US President Donald Trump initially saying fighting in Iran could last "four weeks or so", but on Sunday, he said it could be five weeks or more.
We are starting to understand the intensity of Israel and the US's war plan.
But a clear picture is difficult to paint, because Iran is a place the world is struggling to hear from.
With the internet at best intermittent and largely down, we're having to piece together what's happening in a huge country of around 93 million people - a population whose fears and hardships are being smothered by a lack of communication.
Iran latest: US vows to 'finish war' as Iranian strikes reported across Middle East
On Monday alone Israel’s defence forces said they’d carried out what they call a broad wave of strikes against targets in the heart of Tehran.
A few hours after that statement, a UK-based British-Iranian contact sent me a scant message.
It read: "Update from a friend who spoke with her family inside. Basij (militias) are on the streets with arms and have inspection points.
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"Costs of food is six times the norm. Bombing is very intense. We are happy to hear the noises."
We can't independently verify their message, but it appears to give some sense of what life is currently like inside Iran.
Those who want to see an end to the Iranian regime are banking on Donald Trump's promises of a new dawn and hope these days of fear are worth it.
Flight operations remained largely suspended for a third day, leaving tens of thousands of passengers stranded as aviation faced its biggest test since the COVID-19 pandemic.
The war in the Middle East expanded further on Monday as Israel and the US pounded Iran in a campaign that US President Donald Trump said would probably take several weeks.
Meanwhile, Tehran and its allies struck back against Israel, neighbouring Gulf states and targets vital to the world's production of oil and natural gas.
Iran latest: Follow live updates
Iran's retaliation to US and Israeli attacks has threatened British people across the Middle East.
Around 300,000 Britons are believed to be in countries targeted by Iran, with 102,000 registering their presence with the Foreign Office, as officials worked on contingency plans, including a potential mass evacuation.
Large areas of airspace remained closed across the Middle East amid the deepening conflict between Iran and US-Israeli forces.
Long-haul carriers Etihad Airways and Emirates, based in Abu Dhabi and Dubai, and budget carrier FlyDubai, said they would operate select flights from the country, where air traffic was suspended on Saturday and defence systems have intercepted missiles and drones from Iran.
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Sir Keir Starmer has said the UK government is "looking at all options to support our people" as a small number of flights departed from Abu Dhabi.
Dubai's government told passengers to head to airports only if they were contacted directly, during what it said would be a "limited resumption of operations".
British tourists Gary Gore, 57, and his wife Laura, 48, from Suffolk, are currently holidaying in Doha.
Mr Gore, a partner at a global professional services firm, told Sky News: "We've started off to be an amazing trip in this beautiful hotel with wonderful sunshine and, unfortunately, it's turned into a nightmare from hell."
Ms Gore, a director at a global SaaS company, said the "missiles started on Saturday".
She added: "We're living out of our hotel room. We're packed, ready to go. Missiles are going out all the time. Complete uncertainty.
"We've got our grab bag in case we have to run out of the hotel room."
Brit Terry Dunne, 55, and his wife Joanne, 52, from Bradford, are in Dubai on what was meant to be a week-long holiday.
Mr Dunne, an offshore operative, said they were outside in the pool when the first missiles hit, and staff yelled at them to get inside.
He told Sky News: "Sunday night a boom or a bomb went off outside the hotel, waking us up with security alerts to our phones.
"In the morning, a further explosion happened above the hotel. It must have been shot down, and we all had to evacuate inside the hotel from the orders of the hotel staff."
Mr Dunne said Joanne, a university administrator, had to jump out of the pool and get back in the hotel as there was an explosion a "couple of hundred feet in the air".
Overlooking the scene from his hotel balcony, he said everything in the street appeared deserted, with people being told to keep indoors as much as possible.
Mr Dunne claimed his insurance company was not interested in helping the couple, adding that both the airline and travel company were also refusing to help with accommodation.
The couple have also tried to contact the Foreign Office and the hotel, but have so far received nothing.
Mr Dunne said the couple have had no option but to put a further stay on their credit card, adding they will have to "hope for the best" for now.
Mr Dunne said: "Me and my wife spent all day yesterday in the hotel as advised by the Foreign Office to stay put and keep ourselves safe.
"We've done absolutely nothing, really. Everything's closed, the pool and everything."