WASHINGTON, United States  (AFP) — The United States joined Britain’s allies in Europe and around the world Monday in expelling scores of suspected Russian spies in an unprecedented response to a nerve agent attack.

Washington led the way, ordering out 60 alleged agents, in a new blow to US-Russia ties less than a week after President Donald Trump congratulated Vladimir Putin on his re-election.

Canada, Ukraine and fourteen European Union states matched the move with smaller-scale expulsions, after Britain urged allies to respond to the poisoning of double agent Sergei Skripal.

Russia has denied it was behind the attempted assassination, which left Skripal and his daughter gravely ill in perhaps the first nerve agent attack in Europe since World War II.

And it warned that there would be a tit-for-tat response to those countries “pandering to British authorities” without fully understanding what had happened.

But Western officials made it clear in announcing the expulsions that they share Britain’s assessment that only the Kremlin could have been behind the March 4 incident in Salisbury, England.

White House spokeswoman Sarah Sanders said Washington and its allies were acting “in response to Russia’s use of a military-grade chemical weapon on the soil of the United Kingdom.”

The strong language contrasted with the warm words Trump shared with Putin last week, when he overrode his advisers’ concerns and congratulated his opposite number Putin on his election win.

“The United States stands ready to cooperate to build a better relationship with Russia, but this can only happen with a change in the Russian government’s behaviour,” Sanders said.

US officials said that 48 “intelligence officers” attached to Russian diplomatic missions in the US would be expelled, along with 12 accredited to the United Nations in New York.

Trump’s ambassador to the UN, Nikki Haley, welcomed the move and said: “Here in New York, Russia uses the United Nations as a safe haven for dangerous activities within our own borders.”

In addition, the Russian consulate general in Seattle will be closed, officials said, because of its proximity to US submarine bases and a plant run by private aerospace giant Boeing.

This represents the largest US expulsion of Russian or Soviet agents ever and comes after Trump’s predecessor Barack Obama expelled 35 in late 2016 over alleged election meddling.    

Russia’s foreign ministry warned that the “unfriendly step by this group of countries will not pass without trace and we will respond to it.”

And the Russian embassy in Washington, meanwhile, appeared to hint at what this response would be.

In a tweet, the Russian mission asked followers to vote on which US consulate should be closed, listing those in Vladivostok, St Petersburg and Yekaterinberg as options.

Before the measures were announced, Russia’s Foreign Minister Sergei Lavrov had accused Britain of “feverishly trying to force allies to take confrontational steps.”

Canada confirmed it was expelling four Russian, Ukraine 13 and EU President Donald Tusk said at least 14 member states were kicking out between one and four alleged agents.

An unofficial AFP tally brought the total number of suspects to around 100. They are due to leave in the days and weeks to come.

Britain welcomed its allies’ decision as a diplomatic and moral victory, after concerns that some would prefer not to offend Moscow despite international horror over the attack.

“Today’s extraordinary international response by our allies stands in history as the largest collective expulsion of Russian intelligence officers,” Foreign Secretary Boris Johnson said.

Johnson said it would “help defend our shared security.”

More than three weeks after the attack, which Britain says was carried out by a nerve agent exclusively developed by Russia, the Skripals are still in a coma in hospital.

A British policeman who was exposed to the nerve agent when he responded to the attack on the former Russian officer has now been released from treatment.

A British judge ruled last week that blood samples from former Russian spy Skripal and his daughter Yulia could be taken for testing by the world chemical weapons body (OPCW).