Russia's ambassador to Ireland has launched a scathing attack on the British government.
Yury Filatov said it was taking "absurd, hostile action" following last week's nerve agent attack in southern England.
He said British prime minister Theresa May had engaged in "hype" and "propaganda" for political reasons.
He claimed the UK was illegally preventing Russia from seeing Yulia Skripal (33), who is still seriously ill in hospital with her father, Sergei.
Mr Skripal (66) is a retired Russian military intelligence officer, who was sentenced in 2006 to 13 years in prison, accused of spying for Britain.
The pair were found slumped on a bench in Salisbury, Wiltshire, on March 4.
The chemical used in the attack has been identified as Novichok, a military-grade nerve agent developed by Russia during the Cold War.
Mrs May expelled 23 Russian diplomats, despite President Vladimir Putin denying any involvement in the attack.
On foot of reports that the Russian embassy in Dublin has been involved in spying, Mr Filatov said the claims were part of "a massive propaganda campaign against Russia".
Referencing events in Salisbury, he said: "It's a very sad case and affair.
"Not only because we are taking about harm done to people, not only because of some kind of chemical agent used in European countries, but because of the highly irresponsible way the British government has handled the whole incident."
He said that "from the beginning", the intention of the UK "was not to investigate, but to gain some political points".
"This is a most unfortunate turn of events," he said.
Mr Filatov, who took up his position in Dublin in November, said Moscow would quickly retaliate after the expulsion of its diplomats.
"The British government has taken absurd, hostile action against our diplomatic representation in the United Kingdom," he said.
"I'm sure that, if not today, then certainly very soon we will give an answer to that. It will not go unanswered.
"It's a very worrisome situation when we have a government that is a nuclear power behaving in a most irresponsible, aggressive way."
Tanaiste and Foreign Aff-airs Minister Simon Coveney has condemned the attack in Salisbury.
"The use of chemical weapons, including the use of any toxic weapons, is unacceptable and abhorrent," he said.
"This incident represents a disturbing violation of international law and goes against norms which have long been established.
"We join many states in supporting the UK's efforts to ensure a thorough investigation so that the perpetrators of this crime can be held accountable."