Russia booted 23 British diplomats on Saturday in an escalating tit-for-tat that began when Britain expelled the same number of Russian envoys three days earlier.

Britain initiated the back-and-forth skirmish after accusing Moscow of a deadly nerve agent attack on an ex-Russian spy and his daughter on British soil.

British Prime Minister Theresa May threatened sterner action.

“We will never tolerate a threat to the life of British citizens and others on British soil from the Russian government,” she said at the Conservative Spring Forum in London.

“Russia’s response doesn’t change the facts of the matter — the attempted assassination of two people on British soil.”

Russia also said it might act further if Britain makes more “unfriendly” moves.

A top Russian lawmaker said Britain has no evidence that its spies used a nerve agent to attack ex-Russian agent Sergei Skripal, 66, and his daughter, Yulia, 33.

“We have not raised any tensions in our relations. It was the decision by the British side without evidence,” said Konstantin Kosachev, chair of the foreign-relations committee in the upper house of Russia’s parliament.

Russia also announced Saturday that the British consulate in St. Petersburg and the Moscow outpost of the British Council, a trade and cultural relations group, will be shut down.

A Russian opposition leader urged Britain to act strongly against Vladimir Putin’s government.

“This is absolutely 100 percent necessary,” anti-corruption campaigner Alexei Navalny told The Sunday Times of London (STOL) of May’s moves.

Navalny said expelling diplomats is such a weak move that it is actually a “gift” for Putin, as it “demonstrated that he can assassinate someone on British soil without real consequences.”