Britain pointed the finger at Russian President Vladimir Putin on Thursday for a nerve agent attack on a former Russian spy in England -- a charge that Moscow rejected as "unacceptable".
The leaders of the United States, France, Germany and Canada later said they had "full confidence" in Britain's assessment that officers from Russia's military intelligence service were behind the Novichok attack that nearly killed Russian double agent Sergei Skripal and his daughter Yulia in March.
British Security Minister Ben Wallace said that Putin was "ultimately" responsible for the poisoning in the southwestern city of Salisbury, prompting an angry response from Moscow.
"For us any sort of accusation regarding the Russian leadership is unacceptable," Kremlin spokesman Dmitry Peskov told journalists.
Britain has previously accused Russia of orchestrating the attack, but Moscow denies any involvement and insists it is ready to cooperate in any investigation.
"Neither Russia's top leadership nor those in the ranks below, nor any official representatives have anything to do with the events in Salisbury," Peskov said.
London and its allies expelled dozens of Russian diplomats after the poisoning, prompting a tit-for-tat response from Moscow and plunging relations to a new low.
In a major new development, Prime Minister Theresa May announced Wednesday that police had issued international arrest warrants for the two suspects, identified as Alexander Petrov and Ruslan Boshirov.
She said they were members of Russian military intelligence and acted on orders from a "high level", but Wallace went further when asked if Putin had any responsibility.
"Ultimately he does in so far as he is the president of the Russian Federation and it is his government that controls, funds and directs the military intelligence, the GRU, via his ministry of defence," Wallace told BBC radio.
He added: "I don't think anyone can ever say that Mr Putin isn't in control of his state.... And the GRU is without doubt not rogue."
Wallace also later mocked the GRU's competence, saying the attack was "more Johnny English than James Bond".
He told LBC Radio that the two men "were sent as soldiers to do a mission... they failed in that mission".
Britain briefed the United Nations Security Council Thursday on its latest findings, with Russia vehemently denying involvement.
Russian ambassador Vassily Nebenzia accused Britain of spreading "the same repeated lies" and presenting an "unfounded mendacious cocktail of facts.
"The Russian Federation categorically rejects all unfounded accusations regarding its involvement," he said.
US Ambassador Nikki Haley said everyone should be "chilled to the bone" with the findings.
A joint statement by the leaders of France, Germany, the US and Canada on Thursday said they had "full confidence in the British assessment" as they chose to "reiterate our outrage" over the incident.
"Yesterday's announcement further strengthens our intent to continue to disrupt together the hostile activities of foreign intelligence networks on our territories," they added.
Wallace said his government would seek to "maintain the pressure" on Russia.
Options include "more sanctions", he said.
The government is also reviewing visa applications by wealthy Russians in Britain, and is preparing new powers to stop people at the border if suspected of "malign state activity".
The Skripals survived the poisoning but a local man, Charlie Rowley, picked up a fake perfume bottle containing Novichok weeks later.
Rowley gave it to his girlfriend, Dawn Sturgess, who later died.
British prosecutors accuse Petrov and Boshirov of conspiracy to murder Skripal, attempted murder and the use of a banned chemical weapon.
They said they would not formally demand their extradition, as Russia does not extradite its citizens, but have obtained a European Arrest Warrant for the pair.
Meanwhile, Sergei Skripal's niece on Thursday begged her uncle to call his 90-year-old mother to prove he was alive.
"She is waiting for his phone call. She needs nothing else. She needs one phone call from her son," said Victoria Skripal at an emotional news conference in Russia.