Four Canadian diplomats have been expelled from Russia as the dispute between the Kremlin and the West escalates over the alleged poisoning of a former spy and his daughter earlier this month, according to Global Affairs Canada.

In an email Friday, a spokesperson for Foreign Affairs Minster Chrystia Freeland says the diplomats have been declared unwelcome by the Russian government and efforts were underway for those affected to return to Canada.

Canada is proud to be part of a collective response of 29 nations addressing the <a href="https://twitter.com/hashtag/Salisbury?src=hash&ref_src=twsrc%5Etfw">#Salisbury</a> nerve agent attack, a despicable, heinous and reckless violation of the rules-based order. —@CanadaFP

The move comes after Freeland announced Monday the expulsion of four Russian diplomats from Canada as the U.S. and more than a dozen European allies took similar actions against dozens of Russian diplomats in their own countries.

On Thursday, the Russian Foreign Ministry in Moscow summoned the U.S. ambassador to announce the expulsion of 60 U.S. diplomats in a tit-for-tat response to Washington's move.

The expulsions follow the poisoning of former Russian spy Sergei Skripal and his daughter Yulia in the British city of Salisbury on March 4 by what has been described as a military-grade nerve agent.

A hospital treating the Skripals said Thursday that 33-year-old Yulia was improving rapidly and is now in stable condition, although her 66-year-old father remained in critical condition.

Russia's Foreign Ministry released a statement Friday saying it had informed ambassadors from most of the countries that ordered expulsion of Russian diplomats that an equal number of their diplomats were being expelled.

The foreign ministry statement said 23 countries were informed Friday of expulsions: Australia, Albania, Germany, Denmark, Ireland, Spain, Italy, Canada, Latvia, Lithuania, Macedonia, Moldova, the Netherlands, Norway, Poland, Romania, Ukraine, Finland, France, Croatia, the Czech Republic, Sweden and Estonia.

The statement said Russia would also consider mirror expulsions of diplomats from Belgium, Hungary, Georgia and Montenegro. It did not mention NATO, which is expelling seven Russians.

The expulsion of diplomats from Russia also affects their families; many will be forced to remove their children from school mid-year. (CBC)

The Kremlin has denied any involvement in the attack on Skripal, who served as a double agent for British intelligence before he was arrested by Russian authorities and later transferred to the United Kingdom in a spy swap.

But western governments have nonetheless blamed Russia for what Freeland has described as a "despicable, heinous and reckless act, potentially endangering the lives of hundreds."

The expulsions also affect the diplomats' families, forcing them to take their children out of school in the middle of the year.

"The well-being of Global Affairs Canada employees is our priority," Adam Austen, Freeland's press secretary, said in a statement to The Canadian Press. "We will be making every effort to support those affected and their families with their return to Canada."

Canada's decision to expel the Russian officials earlier in the week was done "in solidarity with our close ally, the United Kingdom," he said.

"This action was in no way aimed at the Russian people, with whom Canada has long and fruitful ties," he said. "Canada remains committed to dialogue and co-operation with Russia on issues where we face common challenges."

Last week, Prime Minister Justin Trudeau said during a Toronto news conference that Russian President Vladimir Putin needs to answer for Russia's role in the nerve gas attack. The next day, the Russian embassy tweeted its response, accusing Trudeau of using confrontational and unproductive rhetoric.