Vladimir Putin put Russia’s nuclear forces on high alert after comments by UK Foreign Secretary Liz Truss and others, the Kremlin has said.
Kremlin spokesman Dmitry Peskov said “unacceptable” remarks were made about possible “clashes” between Nato and Moscow over Russia’s attack on Ukraine.
It is unclear precisely which comments by Ms Truss Russia objects to.
On Sunday, she said if Russia was not stopped, other states may be threatened and it could end in conflict with Nato.
A Foreign and Commonwealth Office source told the BBC: “I don’t think anything Liz has said warrants that sort of rhetoric or escalation.”
They said the foreign secretary had always spoken about Nato as a “defensive alliance” and that the UK needed to support Ukraine.
Echoing comments by Defence Secretary Ben Wallace earlier, the source insisted the UK wanted to avoid “any sort of miscalculation”.
Speaking at a press briefing on Monday, Mr Peskov said: “Statements were made by various representatives at various levels on possible altercations or even collisions and clashes between Nato and Russia.
“We believe that such statements are absolutely unacceptable. I would not call the authors of these statements by name, although it was the British foreign minister.”
Speaking to Sky News’s Trevor Phillips on Sunday, Ms Truss warned that if the Russian president was not stopped in Ukraine, there could be “conflict” between Russia and Nato.
“This long-running conflict is about freedom and democracy in Europe,” she said.
“If we don’t stop Putin in Ukraine, we are going to see others under threat: the Baltics, Poland, Moldova, and it could end up in a conflict with Nato. We do not want to go there.”
The foreign secretary also told the BBC’s Sunday Morning programme that she supported people from the UK who might choose to go to Ukraine to help it fight Russia.
She said it was up to people to make their own decisions and that the people of Ukraine were fighting for “freedom and democracy” not just for their country, but for “the whole of Europe”.
Mr Wallace has since said that people without military training should not travel to Ukraine to fight, warning it was dangerous and there were other ways to help.
Defending Ms Truss, he said she had not she had not been suggesting untrained people should travel to Ukraine.
Downing Street appeared to contradict Ms Truss, saying the “best way” the UK could help Ukraine was by ensuring Mr Putin “fails” in his invasion of Ukraine.
Speaking on Monday afternoon, the prime minister’s official spokesman said: “We fully recognise the strength of feeling about British people wanting to support the Ukrainians following the Russian invasion.
“There’s advice up on travelling to Ukraine, we currently advise against travel to Ukraine.”
Mr Putin said he had placed Moscow’s nuclear forces on “special alert” due to “aggressive statements” by the West, amid widespread international condemnation of his invasion of Ukraine.
His announcement does not mean Russia intends to use its nuclear weapons.
On Sunday evening, Russian state television channel Rossiya 1 used Ms Truss’s comments to illustrate its news flash on the Kremlin’s order and claims of Western aggression.
Russia attacks Ukraine: More coverage
Prime Minister Boris Johnson is set to travel to Poland and Estonia for meetings with his counterparts and Nato secretary-general Jens Stoltenberg on Tuesday, No 10 has said.
Mr Johnson told cabinet ministers earlier the Russian president had made a “colossal mistake” believing his troops would be “garlanded with roses” by Ukrainians, who had instead put up a “fierce resistance” against them.
Earlier on Monday, Mr Wallace said Russia’s heightened nuclear alert was an attempt to “distract” from what was “going wrong” with its assault on Ukraine.
He told BBC Breakfast that Mr Putin’s invasion was not going to plan, with “significant casualties” and protests against it in Russia.
The defence secretary sought to reassure the public on Mr Putin’s order, saying: “We don’t see or recognise in the sort of phrase or the status he described as anything that is a change to what they have currently as their nuclear posture.
“This is predominantly about Putin putting it on the table just to remind people, remind the world, that he has a deterrent.
“We will not do anything to escalate in that area, we will not do anything to feed any miscalculation, we take it very, very seriously.”