Russian Foreign Minister Sergey Lavrov said on Friday Russia would order British diplomats to leave the country in response to Britain's decision to expel 23 staff at the Russian embassy in London.

Lavrov made the comment in answer to a question by a Reuters reporter as to whether Moscow would retaliate with expulsions of its own. "We will, of course," Lavrov replied, without giving more details.

Read more: Russia's conflict-laden foreign policy

Dmitry Peskov, who serves as Russian President Vladimir Putin's spokesman, said that Moscow's response "will be coming shortly."

"We have never encountered this level of discussion on the global stage," Peskov told reporters, adding that he was surprised by London's reaction.

This comes as the UK continues to accuse Russia of being behind a nerve-agent attack on ex-Russian spy Sergei Skripal and his daughter, Yulia, in the southern English city of Salisbury on March 4.

Later on Friday, British Foreign Secretary Boris Johnson said it was "overwhelmingly likely" that Putin himself had ordered the nerve agent attack. 

Continued denial

Russia insists it was not involved, despite Britain's assertion that the nerve agent was one first produced in the former Soviet Union.

Lavrov said Moscow had stopped paying attention to Britain over the spy poisoning allegations. He also said that British Defense Minister Gavin Williamson, who earlier told Russia to "go away and shut up," may lack education.

Meanwhile Kremlin spokesman Peskov described Johnson's claim that Putin had ordered the poisoning as a "shocking and inexcusable breach of diplomatic propriety."

On Thursday, the UK, along with its allies Germany, France and the US, issued a joint declaration, saying there is "no plausible alternative" to Russian involvement.

"This use of a military-grade nerve agent, of a type developed by Russia, constitutes the first offensive use of a nerve agent in Europe since the Second World War," the countries said in the statement.

No 'new Cold War'

NATO Secretary General Jens Stoltenberg on Friday told British broadcaster BBC that "to isolate Russia is not an alternative."

"We don't want a new Cold War, we don't want a new arms race, Russia is our neighbor therefore we have to continue to strive for an improved better relationship with Russia," Stoltenberg said.

"At some point, Russia will understand that it is in its interests not to confront us but to cooperate with us, and we are ready to do so if they respect some basic norms and rules for international behavior."

Planted in Moscow?

In a new development, the newspaper The Telegraph, citing unidentified sources, said the toxin used in the attack had been planted in Yulia Skripal's suitcase before she left Moscow to visit her father.

The paper said investigators were looking into whether an item of clothing, cosmetics or a gift that was opened in Sergei Skripal's house in Salisbury may have been impregnated with the poison.

The Skripals and a police officer who attended the scene remain in hospital in a critical condition.

This article was updated at 1600 UTC.

dm,ls,tj/ng (Reuters, AP) 

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