Russia says it is expelling 150 Western diplomats, including 60 from the US, after the expulsion of its own diplomats over the poisoning of the former spy Sergei Skripal and his daughter in Britain.

Britain and its allies have accused Russia of orchestrating the nerve agent attack on Skripal. Russia has denied the accusations.

Russia says it is also shuttering the US consulate in St. Petersburg.

MOSCOW — Russia on Thursday responded quid pro quo to the wave of Western expulsions of Russian diplomats over the poisoning of a former spy and his daughter in Britain, while a hospital treating the pair said the woman was no longer in critical condition.

Sergei and Yulia Skripal were found unconscious and critically ill in the English city of Salisbury on March 4. British authorities blamed Russia for poisoning them with a military-grade nerve agent — accusations Russia has vehemently denied.

Two dozen countries — including the US, many EU nations, and NATO members — have ordered about 150 Russian diplomats out this week in a show of solidarity with Britain, a massive action unseen even at the height of the Cold War.

Russia's foreign minister, Sergey Lavrov, said at news conference Thursday that Moscow would expel the same number of diplomats from each of those countries in retaliation.

Lavrov added that just as he was making the statement, the US's ambassador to Russia, Jon Huntsman, was invited to the Foreign Ministry, where he was handed a notice that Russia was responding quid pro quo to the US's decision to expel 60 Russian diplomats.

Lavrov said Moscow would also retaliate to the US's decision to shut the Russian consulate in Seattle by closing the US consulate in St. Petersburg.

The Foreign Ministry said the US diplomats, including 58 from the US embassy in Moscow and two from the US consulate in Yekaterinburg, must leave Russia by April 5, and that the US must leave the consulate in St. Petersburg no later than Saturday.

The ministry warned that should the US take further "hostile actions" against Russian missions, Russia would respond in kind.

"We invite the US authorities who are encouraging a slanderous campaign against our country to come back to their senses and stop thoughtless actions to destroy bilateral relations," it said.

Lavrov said the expulsions followed a "brutal pressure" from the US and Britain to force their allies to "follow the anti-Russian course."

He also noted that the job of the international chemical-weapons watchdog was to determine what chemical agent was used to poison Skripal and his daughter, not to verify Britain's conclusions.

Lavrov said Moscow on Monday called a meeting of the secretariat of the Organization for the Prohibition of Chemical Weapons to discuss the case.

Sergei Skripal. ITV News

Meanwhile, the Salisbury NHS Foundation Trust, which oversees the hospital where the Skripals are being treated, said Thursday that Yulia, 33, was "improving rapidly" and now in stable condition.

"She has responded well to treatment but continues to receive expert clinical care 24 hours a day," said Dr. Christine Blanshard, the medical director of Salisbury District Hospital.

Sergei Skripal, 66, remains in critical condition, the hospital said.

Lavrov said Russia would seek consular access to Yulia Skripal now that she had regained consciousness.

Sergei Skripal, a former Russian military intelligence officer, was imprisoned after he sold secrets to British intelligence. He was released in a 2010 spy swap and moved to Britain.

Britain says he and his daughter, who was visiting from Russia, were poisoned with a Soviet-era nerve agent that must have come from Russia.

Police say the two were most likely exposed to the poison on the door of Sergei Skripal's suburban house in Salisbury, where the highest concentration of the chemical has been found.

About 250 British counterterrorism officers are working on the investigation, retracing the Skripals' movements to uncover how the poison was delivered. They have searched a pub, a restaurant, and a cemetery, and on Thursday they cordoned off a children's playground near Skripal's home.

Maria Zakharova, a spokeswoman for the Russian Foreign Ministry, said Thursday that Britain's allegation of Russian involvement in the poisoning was a "swindle" and an "international provocation." She said Russia continued to demand access to investigation materials that Britain had refused to share.

Zakharova charged that Britain, the US, the Czech Republic, and Sweden all had researched the nerve agent that London said was used to poison the Skripals.

She said the Western research into the class of nerve agent, known as Novichok, was reflected in numerous open-source documents of NATO members. Britain and its allies have dismissed previous Russian claims that they possessed that type of nerve agent.