Russia says it is currently considering “retaliatory measures” against Britain, which has threatened to take punitive measures against Moscow over accusations that the Russian state was behind an alleged nerve agent attack on a former Russian spy in southern England.

“After the United Kingdom announced unfriendly actions against Russia, retaliatory measures must be taken, as the Russian Foreign Ministry stated yesterday,” Russian Foreign Ministry spokeswoman Maria Zakharova said on Thursday. “They are currently under consideration and will be taken in the near future.”

Zakharova did not reveal if Britain had already taken any action against Russia.

On March 7, British authorities announced that former double agent Sergei Skripal, 66, and his 33-year-old daughter, Yulia, had been hospitalized after being found unconscious on a bench outside a shopping center in the city of Salisbury. They had reportedly been exposed to a nerve agent.

British police attributed the critical illness of the two to a nerve agent developed by the former Soviet Union, and British Prime Minister Theresa May accused Russia of being responsible.

Moscow has denied any involvement, and some chemical experts have said the nerve agent may have been stolen in the aftermath of the collapse of the former Soviet Union, when security at chemical sites was allegedly lax.

Zakharova said Moscow had sent four notes to the British Foreign Office concerning the poisoning of Skripal, but had received non-committal replies.

“I would like to inform you that the Russian Embassy in London has dispatched several diplomatic notes to the Foreign Office with the goal of starting an active dialog with officials in London over the state of affairs that ensued as a result of the use of poisonous chemicals on British soil,” she said. “Four notes were dispatched in all. In reply, we got non-committal messages meaning nothing.”

Zakharova further said that Moscow had officially expressed readiness to work with British authorities over the case within a legal framework but London had been “unwilling” to cooperate.

Kremlin spokesman Dmitry Peskov had on Thursday denounced Britain’s stance as “irresponsible.”

“These are all signs of a provocation against our country. The positions of the British side seems absolutely irresponsible to us,” Peskov said. “We insist that Russia has no connection to what happened in Great Britain.”

On Wednesday, British Prime Minister May announced plans to expel 23 Russian diplomats in the wake of the attack on Skripal in Salisbury.

UK expels 23 Russian diplomats over nerve agent attack

Britain plans to expel 23 Russian diplomats after an alleged chemical agent attack which London has blamed on Moscow.

France backs Britain

Also on Thursday, French President Emmanuel Macron backed the British allegation that Russia was responsible for the alleged nerve agent poisoning of the former spy, saying there was “no other plausible explanation.”

“Since the start of the week, Britain has kept France closely informed of the evidence gathered by British investigators and of elements demonstrating Russian responsibility in the attack,” Macron said.

“France shares Britain’s assessment that there is no other plausible explanation and reiterates its solidarity with his ally,” he added.

Skripal was found guilty by a Russian tribunal of selling classified information to the UK’s spy agency MI6 and was imprisoned in Russia in 2006. He was exchanged in a spy swap in 2010.

Britain’s National counter-terrorism police have taken over the investigation on the alleged attack and are treating the case as attempted murder.