Russia ordered new cuts Friday to the number of British envoys in the country, escalating a dispute with the West over the poisoning of an ex-spy in Britain.
The massive expulsion of diplomats on both sides has reached a scale unseen even at the height of the Cold War.
Two dozen countries, including the US and many EU nations, and NATO ordered out more than 150 Russian diplomats this week in a show of solidarity with Britain over the poisoning of Russian ex-spy Sergei Skripal and his daughter in Britain that London blamed on Russia.
Moscow has vehemently denied involvement in the March 4 nerve agent attack in the English city of Salisbury and announced the expulsion of the same number of diplomats from each nation.
Scores of foreign ambassadors streamed into the Russian Foreign Ministry in Moscow on Friday to receive the notices given to 23 nations.
The ministry further escalated its response Friday, saying it has ordered Britain to reduce the number of its diplomats in Moscow to the level that Russia has in London.
Analysts said that there were around 35 Russian diplomatic officials left in London after the expulsions.
The ministry said it summoned the British ambassador to hand him a protest over the “provocative and unsubstantiated actions by Britain, which instigated the expulsion of Russian diplomats from various nations for no reason.” It gave London one month to reduce its diplomatic personnel in Russia.
Commenting on the Russian move, a spokeswoman for the British Foreign Office said "it's regrettable but in light of Russia's previous behaviour, we anticipated a response."
"However, this doesn't change the facts of the matter: the attempted assassination of two people on British soil, for which there is no alternative conclusion other than that the Russian state was culpable," she said.
"Russia is in flagrant breach of international law and the Chemical Weapons Convention and actions by countries around the world have demonstrated the depth of international concern."
A hospital treating the Skripals said Thursday that the 33-year-old daughter Yulia was improving rapidly and was now in stable condition, although her 66-year-old father remained in critical condition.
The Russian Embassy said in a tweet: "Good news as Yulia Skripal is reported as recovering well. We insist on the right to see her, in accordance with the 1968 Consular Convention."
Speaking to reporters Friday, Kremlin spokesman Dmitry Peskov insisted that "Russia didn't start any diplomatic wars," and "remains open for developing good ties."
He added that Russia has called a meeting of the international chemical weapons watchdog next week to press for an "unbiased and objective investigation."
Russia has accused Britain of failing to back up its accusations with evidence and refusing to share materials from the probe.
The Foreign Ministry said it told the British ambassador on Friday that Moscow is ready to cooperate in the investigation.
The Russian Embassy in London tweeted a statement by the Russian Foreign Ministry's spokeswoman Maria Zakharova saying that Britain and the US "do most to undermine any trust element in international relations."
Earlier this week, the Russian Foreign Ministry alleged that British special services could have been involved in the poisoning and claimed that Britain, the US, the Czech Republic and Sweden all have researched the class of nerve agent that London said was used to poison Skripal.
Britain and its allies have rejected the Russian nerve agent claims.
On Thursday, the Russian Foreign Ministry in Moscow summoned the U.S. ambassador to announce the expulsion of 60 US diplomats in a tit-for-tat response to Washington's move. Nearly two dozen ambassadors from other countries followed suit Friday.