The former UK prime minister was going from the Ukrainian capital Kyiv to Poland at night when there were drone strikes in the border region, Ukrainian Railways said.
A drone on Sunday struck a passenger train at Yahodyn station, on the Polish border, shortly after the train carrying Mr Johnson had left ahead of schedule.
No casualties were reported, but the strike has prompted a warning about the increasing threat to Europe posed by Russian President Vladimir Putin.
Mr Johnson is reported to have been travelling on the same train as the prime minister's national security adviser Jonathan Powell, former Swedish prime minister Carl Bildt, and one of German Chancellor Friedrich Merz's closest advisers, Gunter Sautter, as well as European diplomats.
The group had been in Kyiv to discuss possible peace negotiations with Russia with the Ukrainian government, according to German newspaper Der Spiegel.
The newspaper said the line between Kyiv and Warsaw had been attacked and a train was struck.
Ukrainian foreign minister Andrii Sybiha said that Russian strikes were hitting closer to NATO and EU member Poland.
"Putin's terror is literally knocking on the doors of the European Union and NATO," he said.
Ukraine's railway operator Ukrzaliznytsia said in a post on Telegram it was "quite possible" that the drone had been aimed at Mr Johnson's train.
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The company said the train "had departed the station earlier than scheduled due to real-time adjustments to train timetables necessitated by the constant threat of Russian strikes".
Mr Johnson condemned the attack as "random and senseless".
He said on X: "I don't know what warped logic drove Putin to blow up a stationary Ukrainian locomotive on the Polish border this morning.
"What we can say for sure is that this is the kind of random and senseless attack Ukrainians are enduring every day - even on civilian railways.
"So far Putin has been responsible for the deaths of 1,700 staff of Ukrzaliznytsia - Ukrainian Railways. They and their daily passengers are absolutely heroic."
Mr Bildt posted a video of a train being evacuated after what appeared to be an explosion on X, and wrote: "This wasn't our train, but the one just minutes after us by the border crossing.
"It was evacuated as the Russian drone approached and no one was hurt. Very good safety system. Our train just had an evacuation warning but could proceed to Dorohusk. The Russian attacks against Ukraine are intensifying."
Polish foreign Minister Radosław Sikorski said the Russian threat was already "inside the house".
Mr Sikorski accused Moscow of waging a "hybrid war" against European nations that went further than cyberattacks, disinformation and espionage to "arson incidents in Poland", "attempts to bring down airliners in Lithuania", and "an attempt to derail a moving train in Poland" - representing an "escalation" in Russian activities.
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Earlier on Sunday, a truck less than a mile from Ukraine's border with Poland was also hit, with operations at the Dorohusk-Yahodyn crossing point being briefly stopped, said border guards.
Russia's defence ministry said it had targeted infrastructure facilitating military cargoes from Europe in western Ukraine.
With the frontline largely static, both Moscow and Kyiv have intensified long-distance strikes in recent weeks to try to shift momentum in the war.
Meanwhile, US President Donald Trump has called on Ukrainian President Volodymyr Zelenskyy to stop targeting Russian diesel infrastructure, saying the attacks were causing a shortage of the fuel.
"I've asked President Zelenskyy not to hit the diesel plants, refineries. Diesel is being driven up by the fact that it's having a hard time coming out of Russia, and that's the case that hurts the world."
A wave of Ukrainian drone attacks on Russian oil refineries in recent months has reduced that country's fuel production, triggering gasoline shortages across the country.
Ukraine, which faces regular Russian attacks on its own energy infrastructure, says refineries are legitimate military targets.
Prominent industry researchers have warned that AI could threaten humanity by the end of the decade.
On Sunday, OpenAI CEO Sam Altman backed a call from Anthropic's chief executive Dario Amodei to install permanent third-party reviewers in "frontier" AI companies.
And Elon Musk, whose SpaceXAI company developed the "Grok" AI, replied to Mr Amodei's post, saying: "Dario is right." Mr Amodei also said companies should slow the rate at which they improve the capabilities of AI models.
Anthropic also revealed that several bad actors had used its Claude AI models for activities including weapons development, cyber operations, surveillance and fraud.
But Dame Wendy Hall, director of the Web Science Institute at the University of Southampton, said AI firms were "busily shooting themselves in the foot at the moment" and could not be left to regulate themselves.
Asked if AI was too advanced to monitor in the same way as the internet and "guardrails" were needed for the technology, she told Sky News: "I hope so, because otherwise we have deep problems.
"I don't think the extinction of the human race, but definitely major catastrophes, unintended maybe, or accidental. But we don't want to have our Chernobyl moment for AI."
Astrophysicist Martin Rees, who co-founded Cambridge University's Centre for the Study of Existential Risk, has since described the risks posed as an even greater threat than climate change.
He told Sky News: “I think it's something that needs to be tackled more urgently because climate change is a real phenomenon and, if it's unchecked for 50 or 100 years, it will change the biosphere and the climate in most countries substantially.
“But it won't kill us all. And, it's not going to happen in a drastic way in a few years.
“Whereas the point is these techniques could any day now create a catastrophe which would for instance, knock out the grid in a large city of Europe, or supply chains could be destroyed.
"And if a city is deprived of energy and food and water for even a few days, that would lead to a breakdown in society. And if this happens simultaneously in many cities around the world, then it may be very hard and very difficult for civilisation in general to recover."
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However, US President Donald Trump appeared to downplay the concerns raised throughout this week while pressed on AI at the Irish Open.
Asked if he would support heavier regulation, he said: "We're leading China in AI. We're the most sophisticated country in the world, and frankly I want to keep it that way because whoever wins AI, wins."
Mr Trump added that there are “very negative forces that are bringing it up that shouldn't be bringing it up and they're bringing up things that won't happen”.
Demonstrators clashed with police after a boat carrying migrants who crossed the Channel in a small boat arrived at Eastney Marina in the city last Sunday.
The protesters blocked roads for hours and vowed to stay all night, with Hampshire Police stepping in to disperse around 200 by around 4am on Monday.
Several police, coastguard and border force vehicles were damaged during the evening and a small number of officers were injured.
Detectives have since combed through hundreds of hours of footage and released images of six men who they say can assist the investigation.
Assistant Chief Constable Tony Rowlinson said: "We have been consistently clear that violence and criminal damage have no part in peaceful protest and we will investigate incidents like this thoroughly and take robust action against those responsible.
"Clearly events on Sunday evening were not peaceful protest, rather violent public disorder, and this will not be tolerated as we work to keep our wider communities in Hampshire and on the Isle of Wight safe.
"I'd urge anyone who recognises the six men pictured to contact us.
"The reality of public order policing is that arrests at the time are not always possible, especially where evidence may need to be reviewed to clearly identify who is responsible for offences."
The boat that arrived in Portsmouth sailed from the Jobourg region of Normandy and reportedly had approximately 140 people on board.
It was met in the Channel by two RNLI boats, who took the migrants to Eastney harbour.
Landings as far west as Hampshire are rare, and the vessel made a much longer journey than most migrant boats.
Police said a 42-year-old man from Paulsgrove, Hampshire, was charged on Friday in connection with the demonstrations last week.
And, a 16-year-old male was arrested in connection with the incident on Saturday and has since been bailed pending further inquiries.
Saturday also saw a further anti-migrant protest, and counter demonstration, in the city but police reported fewer problems.
Last week's disorder unfolded after anti-migrant protests in Dover on 5 September, during which masked men blocked roads to the port.
Approximately 200 people were involved and it caused "significant traffic disruption for several hours", according to Kent Police.
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Nigel Brookes, assistant chief constable of Kent Police, said: "There has been some discussion about the fact that protesters on Saturday wore face coverings.
"To do so is not, in itself, sufficient to establish a criminal offence.
"There is no need to wear a face covering in Kent, if your plan is to peacefully express your views."
Erling Haaland's goal - which handed Man City a 1-0 victory - was initially deemed offside on the pitch before VAR overruled the decision.
Enzo Fernandez was in an offside position as he attempted to play the ball before Haaland scored.
He appeared to impact the defending of Man Utd's Lisandro Martinez by attempting a diving header, despite not touching the ball.
Pro Ref spokesperson has since made an unusual intervention and confirmed that a review of the goal will take place.
It said in a statement: "It was established that Enzo Fernandez did not play the ball and therefore that makes any offside offence subjective, however, on this occasion, the VAR did not recognise the likely impact of his position and should have recommended an on-field review.
"Contact has been made with Manchester United this evening to acknowledge what we deem is an error of judgement. A review of the incident will take place."
Haaland jokingly told Sky Sports that he "took it a bit personally" that referee Michael Oliver thought he was offside in a post-match interview.
He went on: "I looked over to Enzo, the gaffer...he gave me a thumbs up and I kind of knew that it was a goal. So I kind of prepared myself a bit to go and celebrate."
Manchester United coach Michael Carrick previously said it was "worrying" that the goal was allowed to stand.
He also claimed there were no grey areas when it came to determining whether Fernandez had interfered with play.
Carrick said: "I can't understand how we are trying to help referees - putting so many layers behind them, so many people, so many bodies, so many screens and so many offices, to try to come up with the right decisions - and if that's how the rule is interpreted, that you're not interfering with play because you have thrown yourself at the ball six yards from goal and pretty much nearly touched it, it's worrying if that's how the game is seen by those who are officiating it."
United were playing with a man advantage after City's Phil Foden was sent off in the 23rd minute after kicking midfielder Bruno Fernandes.
The result left them with just four points from their opening four Premier League games.
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Former United defender Gary Neville also expressed confusion at the decision.
He said on Sky Sports: "I'm going to need the offside law explaining to me, because that has lost me, I have to say. I do think when they look back on this, they will recognise they got it wrong.
"He'll be nervous, (referee) Michael Oliver, as will (all) the officials, about this goal."
But Housing Secretary Angela Rayner has warned that the funds could be retrospectively capped if they fell foul of new laws on political donations.
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Reform was given two seperate £36m donations by two crypto billionaires, Christopher Harborne and Ben Delo.
Speaking to Sunday Morning with... Rachel Johnson on Sky News this morning, Reform's economy spokesperson Robert Jenrick said the donations were a "breakthrough moment" for the party, which will enable Reform to be "battle ready" for the next general election, and to do work to "prepare for government".
However, speaking on the same programme, Rayner - who is the government minister in charge of democracy and elections - said that any action taken following government plans to curb donations from Brits overseas "will be backdated".
She added that donors who were based overseas and who have "recently returned to the UK... are also within the scope" of a review of donations rules.
But she refused to say directly whether the two £36m donations to Reform could be capped.
Rayner said Labour is legislating to ensure "secure elections that are for the people, and that you can't buy your way into our democracy".
The Representation of the People Bill, which passed the House of Commons in earlier this month and will be debated by the House of Lords on Monday, includes proposals to cap donations made by Brits based overseas at £100,000.
The cap would also apply for the first year of those donors moving back to the UK. These measures would be backdated to March.
Harborne was thought to be living in Thailand, while Delo is reported to have recently moved back to the UK from Hong King.
But Sky's deputy political editor Sam Coates has been told that Harborne and Delo both moved back to the UK before the March cut-off, meaning their mega donations would not be in scope of being capped.
A Reform source said the party is "100% confident both are legal and won't ever have to be handed back".
Asked whether the public will see Reform as "in hock" to the two crypto billionaires, given the size of their donations, Jenrick told Sky News that was "complete nonsense", and that he had "never spoken to either these individuals about cryptocurrency".
"They've asked nothing in return for their donations," he added, pledging that neither Delo or Harborne would receive honours in return for their donations, should Reform enter government after the next election.
Speaking on the same programme, Conservative shadow foreign secretary Tom Tugendhat said that while he welcomes donors "supporting political activity", every political party "is responsible for checking the sources of their own donations".
The two sizeable donations - the biggest in UK political history - are the latest chapter in ongoing stories about Reform's finances.
Party leader Nigel Farage previously received a £5m personal gift from Harborne made in early 2024. He is currently under investigation by the parliamentary commissioner to standards over whether he should have declared the gift when he became an MP in July 2024. Farage denies any wrongdoing.