Allies of the U.S. and U.K. are following suit in expelling Russian diplomats in retaliation for Moscow's alleged poisoning a former Russian spy and his daughter in the United Kingdom.

At least 21 nations — mainly from Europe — have ordered more than 135 Russian diplomats to leave their nations.

Russia is considered the most likely suspect behind the chemical weapon attack on former Russian spy Sergei Skripal and his daughter earlier this month.

"Together we have sent a message that we will not tolerate Russia’s continued attempts to flout international law and undermine our values," British Prime Minister Theresa May told Parliament on Monday.

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She called the joint move the "largest collective expulsion of Russian intelligence officers in history."

The U.K. government expelled 23 Russians last week after an investigation led the government to believe the nerve agent attack was carried out by Russia.

On Monday, President Trump announced that he would kick 60 Russians diplomats out of the country.

"With these steps, the United States and our allies and partners make clear to Russia that its actions have consequences," White House press secretary Sarah Huckabee Sanders said in a statement.

The U.S. and European allies carefully planned the timing of their announcements for maximum effect, The Associated Press reported.

Moscow has denied responsibility for the attack and threatened to retaliate, suggesting it would expel an equal number of diplomats currently in Russia.

The Russian Embassy in Washington, D.C., responded to the ouster by carrying out a Twitter poll asking followers to choose which of three U.S. consulates it should close.

Trump’s willingness to expel Russians marks his first direct retaliation against the Kremlin for the poison attack.

Last week, the president ignored his advisers by calling Putin to congratulate him on his reelection that international organizations criticized for vast irregularities.

Trump did not confront Putin on the attack, even though his aides instructed him to do so.