UK foreign secretary Boris Johnson has said he believes it is "overwhelmingly likely" that the poisoning of former spy Sergei Skripal and his daughter Yulia in Salisbury can be traced back to Russian President Vladimir Putin.
Johnson joins prime minister Theresa May who on Monday said it was "highly likely" Russia is responsible for the nerve agent attack. The US, France, and Germany have also condemned Russia over the incident.
Speaking to journalists in West London on Friday, Johnson was keen to point out that the UK had nothing against Russia, and that there was to "be no Russophobia" following the poisoning of Skripal and his daughter, but firmly laid the blame for the attack with the Kremlin.
"Our quarrel is with Putin's Kremlin and with his decision, and we think it is overwhelmingly likely that it is his decision to direct the use of a nerve agent on the streets of the UK," Johnson said.
Putin's spokesman Dmitry Peskov described Johnson's statement as a "shocking and inexcusable breach of diplomatic propriety", according to Russian news agencies.
"We have repeatedly said that Russia has no relation to that," he said.
Following May's condemnation of Russia over the attack earlier this week, Russia has demanded samples of the nerve agent that is believed to have poisoned Skripal and his daughter Yulia.
Foreign Minister Sergey Lavrov said on Tuesday that Moscow will cooperate with the investigation only if Britain allows it to see samples of the substance — but stressed that Russia is "not to blame" for the incident.
He claimed that Russia's requests for the substance have been rejected, which he described as a violation of the Chemical Weapons Convention.
His remarks come in response to British prime minister Theresa May, who said on Monday it is "highly likely" that Russia is responsible for the poisoning of former spy Sergei Skripal and his daughter Yulia.
Speaking in parliament, May said it was clear the substance that has left Skripal and his daughter in a critical condition was "a military-grade nerve agent of a type developed by Russia".
"This is part of a group of nerve agents known as ‘Novichok’," May added.
The Russian ambassador has been summoned to the Foreign Office to explain how Skripal and his daughter came to be poisoned, for which May said the government believed there could be two possibilities:
"Either this was a direct act by the Russian state against our country," May said.
"Or the Russian government lost control of this potentially catastrophically damaging nerve agent and allowed it to get into the hands of others."
If Russia does not respond by the end of Tuesday, May said the UK government would consider the attack an "unlawful use of force by the Russian state against the United Kingdom".
"This attempted murder using a weapons-grade nerve agent in a British town was not just a crime against the Skripals," May added.
"It was an indiscriminate and reckless act against the United Kingdom, putting the lives of innocent civilians at risk. And we will not tolerate such a brazen attempt to murder innocent civilians on our soil."
The PM's spokesperson said May would chair a national security council on Wednesday morning to consider Russia's response. It is understood that the PM is preparing to update MPs on Wednesday afternoon, after Prime Minister's Questions.
Earlier on Monday, the Russian embassy in London accused the British government of orchestrating a media campaign to link the poisoning of former spy Skripal and his daughter to the Russian state.
In a statement released on Monday afternoon, the embassy's press secretary said Russia was "outraged" by supposed attempts to implicate their country in the attempted murder, and warned of serious consequences for the long-term relationship between the two nations.
Last week, foreign secretary Boris Johnson said he did not want to point any fingers, but called Russia a "malign and disruptive force".
The embassy's statement said the incident had "become quite a negative factor for the relations between our countries due to the unfounded accusations against Russia advanced by the media".
Sergei Skripal, 66, and Yulia Skripal, 33, who were found slumped on a bench in the English city of Salisbury on Sunday 4 March, remain in a critical but stable condition. A police officer who attended to them was also hospitalised, and is conscious in a serious but stable condition.
The crime shares similarities with deaths previously linked to the Russian state, such as the radioactive poisoning of former British spy Alexander Litvinenko in 2006.
"We would like to stress once again that we are outraged by the anti-Russian media campaign, condoned by the Government, that influences the investigation and has a psychological effect on British residents," the embassy's statement said.
"Our compatriots and British nationals of Russian origin are worried about their future in this country. UK-based Russian journalists are receiving threats.
"Current policy of the UK Government towards Russia is a very dangerous game played with the British public opinion, which not only sends the investigation upon an unhelpful political track but also bears the risk of more serious long-term consequences for our relations."
The embassy said it had asked the UK's Foreign Office for information on the health of the pair the day after they fell ill, but was not given any further information.
"The investigation is being concluded in a non-transparent manner ... for the Russian side [and] for the public. Quite naturally, this is a source of concern," the embassy said.
Russian state TV stations have been quick to dismiss any suggestion of Russia's involvement in the Skripal case. The flagship Vesti Nedeli (News of the Week) show on the Rossiya 1 channel went so far as to implicate the UK itself in the crime.
Presenter Dmitry Kiselyov told viewers: "They tried to pin the blame on Russia, but if you think it through, the poisoning of the GRU [military intelligence] colonel was only advantageous to the British.
"As a source, Skripal was completely wrung out and of little interest. But as a poisoning victim, he is very useful. Why not poison him? It’s no big deal. And with his daughter to make it more heart-wrenching for the public."
On Sunday, the show also alleged that the UK was somehow behind Skripal's poisoning, because it wanted to engineer a boycott of the World Cup in Russia this summer.
Zizzi, the Italian chain restaurant where the Skripals ate on the afternoon they became ill, said the branch's 24 staff are on full pay and have been offered work elsewhere in the group.