Russia on Thursday announced a mass expulsion of US diplomats and the closure of the US consulate in Saint Petersburg in retaliation to coordinated moves by Western countries to isolate Moscow in the wake of the poisoning of a former double agent in Britain.

Russian Foreign Minister Sergei Lavrov said Moscow would expel 60 US diplomats and close Washington's consulate in Saint Petersburg in a tit-for-tat response to the expulsion of its envoys across three continents.

In Washington, the State Department said there was no justification for the Russian move and that the United States "reserves the right to respond."

"It's clear from the list provided to us that the Russian Federation is not interested in a dialogue on issues that matter to our two countries," spokeswoman Heather Nauert said of the expelled diplomats.

"I want to remind you that there is no justification for the Russian response. Our actions were motivated purely by the attack on the United Kingdom, the attack on a British citizen and his daughter.

"Remember, this is the first time that a weapons-grade nerve agent, Novichok, has been used outside of war on allied soil."

White House Press Secretary Sarah Sanders said Russia's expulsion of US diplomats marks a "further deterioration" in relations between the two countries, but like Nauert defended similar moves by Washington and its allies.

"Russia's response was not unanticipated, and the United States will deal with it," she said.

Lavrov said the US Ambassador to Russia Jon Huntsman had been informed of "retaliatory measures", which include "the expulsion of the equivalent number of diplomats and our decision to withdraw permission for the functioning of the US consulate general in Saint Petersburg."

Over 150 Russians expelled

Earlier, Washington had ordered 60 Russia diplomats to leave the country and shut down the Russian consulate general in Seattle.

In all, more than 150 Russian diplomats have been ordered out of the US, EU members, NATO countries and other nations in coordinated action against Moscow which they accuse of poisoning ex-spy Sergei Skripal and his daughter Yulia in a nerve agent attack in the English city of Salisbury on March 4.

On Thursday, the hospital where the two are being treated said that Yulia, 33, was "improving rapidly and is no longer in a critical condition", while 66-year-old Sergei remained in a critical but stable condition.

Britain has said it is "highly likely" that Russia was responsible for the attack using a nerve agent developed in the Soviet Union, but Russia has angrily denied any involvement.

The Russian foreign ministry said that 58 diplomats from the US embassy in Moscow and two from the consulate in the city of Yekaterinburg have to leave Russia by next Thursday.

And the US consulate general in Saint Petersburg will have to be vacated by Saturday.

Moscow warned that Huntsman's suggestion -- made on Russian RBK television -- that the US could also freeze Russian state assets would lead to "further serious deterioration in our relations."

And it warned that it could take further measures in response if Washington "continued hostile actions" against the Russian embassy and consulates.

"We have suggested that the US authorities, which have encouraged and inflated a campaign of slander against our country, should come to their senses and cease thoughtless actions that destroy bilateral relations," the ministry said.

'Pressure from US and Britain'

Lavrov said Russia was also mulling tit-for-tat responses to the other countries that have expelled its diplomats.

"As for the other countries, it's also all symmetrical measures as to the number of people who will be leaving Russia from diplomatic missions, and that's all so far," Lavrov said.

Indeed, the measures might "not only" be symmetrical, he said.

Lavrov said Russia was reacting to "absolutely unacceptable actions that are taken against us under very harsh pressure from the United States and Britain under the pretext of the so-called Skripal case."

He accused London of "forcing everyone to follow an anti-Russian course."

Lavrov said Britain had informed Moscow of the state of health of Yulia Skripal on Thursday and that Russia had asked again for access to her as a citizen.

He said Moscow wanted to "establish the truth" over the poisoning and accused Britain of "making mockery of international law."

Russia had asked for a meeting with the executive council of the Organisation for the Prohibition of Chemical Weapons on Tuesday to ask questions to "establish the truth", he said.

"We are counting on our Western partners not evading an honest conversation," Lavrov said.

After the poisoning, Britain reacted by announcing it would expel 23 Russian diplomats, suspend high-level diplomatic contact with Moscow and not send royals to the 2018 football World Cup hosted by Russia.

Russia then responded by closing a British consulate in Saint Petersburg and closing the British Council educational and cultural organisation.Russia's expulsion of 60 US diplomats and shuttering of one of its consulates marks a "further deterioration" in relations between Washington and Moscow, the White House said Thursday.