The US secretary of state added that while the talks are progressing - with Pakistani representatives travelling to Iran on Thursday - Washington is dealing with "a system that itself is a little fractured".
Mr Rubio added that any diplomatic deal would be "unfeasible" if Iran imposes a toll on the Strait of Hormuz.
"No one in the world is in favour of the tolling system," he said. "It can't happen. It would be unacceptable.
"It would make a diplomatic deal unfeasible if they were to continue to pursue that. So it's a threat to the world if they were trying to do that, and it's completely illegal."
Mr Rubio was speaking to reporters in Florida on Thursday as he boarded a flight to Sweden, where he will meet with NATO foreign ministers.
The Strait of Hormuz, which is a conduit for one-fifth of global oil exports, has effectively been blocked by Tehran since the US and Israel launched strikes on Iran on 28 February. The stand-off escalated last month when the US began blocking Iranian ports.
Iran has claimed sovereignty over the strait, saying it will only fully reopen the waterway if it gets to charge commercial vessels tolls for passing through.
The disruption has had a wide impact on global economies, sending energy prices soaring and hitting government borrowing.
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A shaky US-Iran ceasefire has been in place since early April, but both the Trump administration and Iranian officials have repeatedly threatened to resume attacks.
Donald Trump said in a Truth Social post earlier this week that he had told the US military "to be prepared to go forward with a full, large-scale assault of Iran, on a moment's notice" if a deal isn't reached.
The US president echoed his previous comments as he spoke at the White House on Thursday, telling reporters he will "have to do something very drastic" if Iran refuses to guarantee it will not acquire a nuclear weapon.
Meanwhile, Iran's Revolutionary Guard threatened that it would "extend the war beyond the region" if the US attacks Iran again.
Health alerts have been issued as the country braces for a heatwave from Friday through to next week.
Sky News weather presenter Jo Wheeler said the UK could see the hottest day of the year so far - smashing the 26.6C (79F) at London's Kew Gardens on 8 April.
Meanwhile, the 32.8C (91F) record for May set in the capital's Camden Square in 1922 could be surpassed.
Over the weekend, temperatures in the UK are expected to exceed those forecast in Mediterranean hotspots including Mykonos, Rhodes and Santorini.
On Friday, the mercury is forecast to hit 29C (84F) - with a 20% chance of 30C (86F) - across the East Midlands, East Anglia, London and north Kent.
On Saturday, temperatures of 30C (86F) - with a 20% chance of 32C (89F) - are expected in Greater London.
While on Sunday they could hit 31-32C (87-89F) - with a 20% chance of 34C (93F) - across south and southeast England and the South Midlands.
Monday looks set to be even hotter, with 32-33C (89-91F) - with a 50% chance of 34C (93F) - forecast for south England and the Midlands.
And on Tuesday, 31-32C (87-89F) - with a 20% chance of 34C (93F) - is expected in south England.
See the five-day forecast for your area
The UK Health Security Agency has issued heat health alerts covering much of the Midlands, eastern and southeast England.
Officials are warning of "minor impacts" across health and social care services, including a greater risk to life for vulnerable people.
The Alzheimer's Society said people with dementia are likely to be more vulnerable in warmer conditions.
The charity outlined ways to support loved ones or neighbours with dementia by leaving drinking water within easy reach and ensuring they opt for light-coloured, airy clothes, stay out of the sun between 11am and 3pm, take cool showers and keep blinds closed.
The British Heart Foundation said heart patients also face potential dangers in the heat and should take extra precautions to minimise health risks.
Asthma + Lung UK also issued advice for those with lung conditions, including taking any preventer inhaler as prescribed and keeping a reliever inhaler handy to treat symptoms quickly.
Karen Spillett, deputy head of health advice at the charity, said: "Hot weather can affect breathing and make symptoms like breathlessness and wheezing worse for people with asthma, COPD (chronic obstructive pulmonary disease) and other lung conditions.
"Warmer weather often causes rising pollen levels and increases the presence of a toxic air pollutant called ozone.
"These can make it harder to breathe and put people at risk of a flare-up or asthma attack, which can be life-threatening and require emergency care."
There may also be an increased danger of water-related incidents such as drowning and cold-water shock.
The RNLI said choosing a lifeguarded beach, swimming between the red and yellow flags, and dialling 999 or 112 and asking for the coastguard in an emergency can make all the difference in staying safe on the coast.
Samantha Hughes, RNLI water safety partner, said: "If you find yourself in difficulty in the water, try to remain calm and remember float to live: lean back with your ears submerged, extend your arms and legs, and float until you can control your breathing and wait for help to arrive or before moving to safety."
Campaign group River Action additionally warned of the health risks posed by poor water quality, even in designated bathing spots.
The Royal Society for the Prevention of Accidents (RoSPA) and Children's Burn Trust are also urging people to take care if they are planning a barbecue.
Rebecca Guy, senior policy manager at RoSPA, said: "Barbecues cause serious burns every year, often because people underestimate how hot they stay long after cooking has finished.
"Children should be kept well away from barbecues at all times, and disposable barbecues must never be moved or put in bins until they are completely cold.
"Simple steps like safe placement, supervision and proper disposal can prevent life-changing injuries."
A heatwave in the UK is officially recorded when an area experiences at least three consecutive days with temperatures meeting or exceeding the region's threshold.
Steve Kocher, deputy chief forecaster at the Met Office, said: "Temperatures will climb through the weekend, especially in the south, where 30C is likely to be recorded on Saturday and 32C on Sunday.
"Temperatures are forecast to peak on Monday when we could see 33C recorded in southern England and the Midlands.
"It is likely that the May and spring UK temperature records will be broken over the bank holiday weekend, with forecast temperatures surpassing the existing record of 32.8C.
"As well as it being hot, there will be lots of dry and sunny weather for much of the UK.
"There will, however, be more cloud and some showers in Northern Ireland and western Scotland through the weekend.
"With relatively low sea surface temperatures, there is also likely to be some low cloud and sea fog clinging closely to western coasts."
Valdo Calocane killed University of Nottingham students Barnaby Webber and Grace O'Malley-Kumar, both 19, as well as 65-year-old caretaker Ian Coates, and attempted to kill three more people in the June 2023 attacks.
Nottingham University Hospitals (NUH) NHS Trust said on Thursday that "11 members of staff have been dismissed and a further 14 have had actions taken against them".
It added that further investigations are ongoing.
Barnaby's mother, Emma Webber, reacted to the news in an interview with Sky News, saying: "This was just gross voyeurism at the worst possible level. This wasn't uncovered by any due diligence, this was uncovered because we insisted upon it.
"It's horrifying. It's so intrusive and traumatising. At least some action has been taken, but not all."
The decision to sack the staff comes as a public statutory inquiry into the killings continues.
The trust said that it had been investigating the breach since starting investigations in early 2025.
Actions taken so far include two first written warnings, 12 final written warnings and 11 staff dismissed, it said.
"Staff included in these investigations include doctors, nurses, registered medical professionals and admin and clerical colleagues," the statement added.
The trust said it would now consult with regulators such as the Nursing and Midwifery Council (NMC) and General Medical Council (GMC), both of which have powers to strike staff off medical registers.
The trust has also informed the Information Commissioner's Office (ICO) and Nottinghamshire Police.
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'I am truly sorry'
Dr Manjeet Shehmar, medical director at NUH, said: "The families of Ian, Grace and Barnaby have had to endure much pain and heartache, and I am truly sorry that the actions of some of our staff have added to that.
"To access the medical records of our patients without a legitimate reason is totally unacceptable and we are doing all we can to identify where and how that has happened.
"I hope that the families, staff and our communities feel reassured by the outcomes so far, that we are taking this seriously and will continue to do so.
"We know that the vast majority of our staff understand that appropriate access is a fundamental principle of our duty of care and know that it is essential that access to patient records is lawful, justified and directly related to their role.
"By accessing records inappropriately, staff are damaging the valuable contributions made by those colleagues providing care for those patients.
"In those cases where it does happen, I hope that this is a very clear reminder that we will take appropriate action."
Further investigations are ongoing into inappropriate access, including into the files of surviving victims, including Wayne Birkett, Sharon Miller and Marcin Gawronski, the trust said.
Nurses referred to regulator
As the inquiry continued on Thursday, it heard three nurses have been referred to the NMC in relation to Calocane's case.
Diane Hull, chief nurse with the NUH trust, who took up her post a month after the attack, was quizzed about disciplinary processes.
Rachel Langdale KC, counsel to the inquiry, asked her: "In relation to VC's case, we understand one doctor has self-referred. One doctor, we were told yesterday by the medical director, the GMC indicated did not meet the referral criteria.
"Have any of those been referred by the trust, as far as you're aware, to the GMC?"
Ms Hull responded: "I don't know about doctors. I can tell you about nurses.
"Three people have been referred to the NMC. We regularly consult with the NMC.
"We've also committed… to do a further review of professional standards and practice following the inquiry as well."
Two women anonymously alleged they were raped by their on-screen husbands when they appeared on the Channel 4 show, and former participant Shona Manderson accused her on-screen partner of sexual misconduct, while speaking in a BBC Panorama documentary.
All three men deny the allegations against them.
In a statement a spokesperson for Tui UK and Ireland said: "Following the broadcast of the Panorama programme and discussion with Channel 4, we have taken the decision to end our sponsorship of Married At First Sight."
The spokesperson confirmed the travel operator had paused its sponsorship of the UK and Australian versions of the show after the accusations featured in the Panorama episode on Monday.
Last month, Channel 4 launched a review into contributor welfare shortly after being contacted by the BBC about the accusations featured in the Panorama episode.
Channel 4's chief executive, Priya Dogra, has said reports the show had been cancelled are "wholly inaccurate" and "no decision has been made" regarding the broadcast of the next series.
New episodes of MAFS UK have been "substantially filmed" and are currently being edited, Channel 4's chief content officer Ian Katz has said.
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On Wednesday, MPs on the Culture, Media and Sport Committee wrote to Channel 4 and Ofcom about their response to allegations raised in the BBC documentary.
Committee chairwoman Dame Caroline Dinenage called the accusations "horrifying" and added: "Both Channel 4 and Ofcom, as the broadcasting regulator, have urgent questions to answer."
The letter to Channel 4 also asked about its complaints process for contestants on the programme, as well as the steps being taken to ensure the allegations were fully investigated, along with the review announced by the broadcaster.
It also asks the broadcaster about its approach to duty of care to participants on its other reality TV programmes.
On Tuesday, the government said there must be "consequences for criminality or wrongdoing" following the MAFS allegations.
The Metropolitan Police urged potential victims of sexual assault on the TV show to get in touch.
Southampton Crown Court heard two girls were raped in two separate incidents in Fordingbridge, with the first attack taking place on 26 November 2024 and the second on 17 January 2025.
A 15-year-old boy was sentenced to a youth rehabilitation order (YRO) for three years with 180 days of intensive supervision and surveillance (ISS) for the rape of each of the two girls and two indecent images charges.
The court heard that he had been diagnosed with ADHD as well as "long-standing anxiety".
A second 15-year-old was given the same sentence for three charges of rape against each of the two victims and four counts of taking indecent images in relation to filming of the incidents.
The court was told that he had an IQ of the "bottom 1% of his contemporaries" and had been diagnosed with ADHD.
A third boy, aged 14, was given a YRO for 18 months for two charges of rape in the January incident by encouraging the second defendant and an offence of indecent images.
He was described as having "mild cognitive impairment".
Judge Nicholas Rowland told the defendants: "I have to remember that you are not small adults. I have to think how likely you are to do serious things again and I need to make sure you do not do serious things again in the future."
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Explaining his sentence, he added: "I should avoid criminalising these children unnecessarily and understand the effects of their behaviour and support their reintegration into society."
He added that "peer pressure played a large part in what went on".
The victim of the first incident, who was 15 at the time, attended the sentencing and read out her victim impact statement.
She also read out a poem which she wrote and was directed to her attackers.
She said: "I was caught off-guard, I never want that to happen again, I will never get that innocence back again."
The poem included the line: "All I want to do is die, I no longer have fear for when that comes."
She added: "No one deserves the trauma of being raped."
In a statement read on behalf of the second victim, she said her school attendance had suffered and added: "I often feel overwhelmed, anxious and emotionally exhausted to the point where sitting in a classroom becomes unbearable."
She described suffering nightmares and struggling to sleep and added: "I feel ashamed, insecure and uncomfortable in my own body."
Jodie Mittel KC, prosecuting, told the trial that the girl in the November incident had visited the first defendant after meeting him on Snapchat.
The prosecutor said that after performing sex acts on the boy, who was then 14, she became "scared and anxious" when the second defendant joined them with a third boy who was not charged.
Ms Mittel said that the girl felt "cornered and trapped" and "petrified" as the two defendants raped her while the incident was filmed.
Ms Mittel said that afterwards, videos of the incident had been sent around and other people made jokes about her and she received messages calling her a "slag".
The complainant in the January incident, who was 14 at the time, was raped in a field near to Fordingbridge recreation ground while the incident was also filmed.