Russia should "go away" and "shut up", Defence Secretary Gavin Williamson has said, following Russian threats to expel British diplomats in a growing tit-for-tat row over the poisoning of former spy Sergei Skripal.
His comments come as Prime Minister Theresa May visited Salisbury, the scene of the attack that left Mr Skripal and his daughter critically ill in hospital.
Speaking in Salisbury Mrs May said: "We do hold Russia culpable for this brazen and despicable act that has taken place on the streets of what is such a remarkable city."
During her visit the prime minister also spoke to Detective Sergeant Nick Bailey, the third attack victim, who remains in hospital after being exposed to the never agent when he went to aid the Skripals.
Downing Street declined to reveal the content of what the spokesman said was a "private conversation".
Earlier Mrs May visited the scene where the Skripals were found and met local businesses and members of the emergency services, escorted by Kier Pritchard, the chief constable of Wiltshire police, and Salisbury MP John Glen.
The prime minister's visit comes a day after she announced the decision to expel 23 Russians after Moscow failed to meet a deadline to explain the nerve agent attack.
Russia has threatened to throw out British diplomats in response, with Russian news agency RIA reporting Sergei Lavrov, the Russian foreign minister, as saying the expulsions would come "very soon, I promise you that".
Mr Lavrov also accused the UK of "fanning anti-Russian rhetoric bordering on hysteria" to win support from its allies.
Another Russian news agency, Tass, quoted Russia's presidential spokesman Dmitry Peskov as saying President Vladimir Putin would personally choose how Russia retaliates.
"There is no doubt that he will choose the variant that best of all corresponds to the interests of the Russian Federation," Mr Peskov said.
Mr Putin's office later issued a statement saying the Russian president had held an "in-depth discussion" with the country's security council on the matter.
But the threats appear to have left the government unfazed.
Mr Williamson, who was in at Porton Down to announce a multimillion-pound investment in a new specialist defence centre, said that if Russia went through with its threat "we will consider it carefully and we'll look at our options", but he said that "frankly Russia should go away, should shut up".
He said that UK relations with Russia were "exceptionally chilly", but both he and his colleague Foreign Secretary Boris Johnson have played down talk of a new Cold War.
Mr Johnson, speaking separately, said: "I don't want to see a new Cold War ... but there's no questions our relations with Russia are going through a very difficult phase," he said.
The ministers' Cabinet colleagues have also been busy. Home Secretary Amber Rudd was chairing a meeting of the government's Cobra emergencies committee in London to discuss the latest situation.
And Environment Secretary Michael Gove led a cross-governmental ministerial recovery group looking at support which will go to the people of Salisbury in the aftermath of the incident.
From the Opposition, Labour leader Jeremy Corbyn defended comments by his team that had appeared to raise doubts about who was responsible for the attack, acknowledging "the evidence points towards Russia on this".
Pressed on comments made by his shadow defence secretary Nia Griffith, who said it would have been "easier" for Labour if Mr Corbyn had made clear he supported the expulsion of the Russians.
Speaking in Carlisle, Mr Corbyn told reporters: "I was extremely definite yesterday that I totally condemn this attack. The perpetrators must be brought to justice."
The UK has received backing from its ally the US, with a statement from the White House saying the US "shares the United Kingdom's assessment that Russia is responsible for the reckless nerve agent attack".
The White House also backed the UK's decision to expel Russian diplomats, although observers noted that despite its strong language, the White House statement did not come directly from President Donald Trump who has been historically reluctant to criticise his Russian counterpart.
Speaking separately to reporters on Thursday, Mr Trump said it "looks like" Russia was behind the Salisbury incident.
"It certainly looks like the Russians were behind it, something that should never ever happen," he said. "We are taking it very seriously as, I think, are many others."
Britain's other allies have also stepped forward. Downing Street said on Thursday that France "completely shares" the UK assessment of the Salisbury attack, following an early morning call between Prime Minister Theresa May and France's President Emmanuel Macron.
A statement posted following the call by the French Embassy said: "France shares the assessment of the United Kingdom that there is no other plausible explanation and expresses once again its solidarity regarding its ally."
In Brussels, Nato states were briefed by UK National Security Adviser Sir Mark Sedwill.
Jens Stoltenberg, the Nato secretary general, said: "Russia has integrated conventional and nuclear warfare in its military doctrine and exercises.
"This blurring of the line between nuclear and conventional lowers the threshold for Russia's use of nuclear weapons. And the blurring of the line between peace, crisis, and war is destabilising and dangerous."
The row has also been playing out at the UN, where Britain called on the Organisation for the Prohibition of Chemical Weapons (OPCW), the international chemical weapons watchdog, to verify its findings that Moscow is behind the Salisbury incident.
Mr Johnson confirmed the UK will submit a sample of the nerve agent to OPCW for it to carry out its own tests.
The use of a military-grade nerve agent in Salisbury "constitutes the first offensive use" of a nerve agent in Europe since the Second World War, according to a joint statement from France, Germany, the United States and Britain said.