President Donald Trump is preparing to expel dozens of Russian diplomats from the U.S., following the poisoning of a former Russian spy in the U.K., Bloomberg News reported on Saturday.

The expulsions will likely be announced on Monday, sources familiar with the matter told Bloomberg, but the decision is still being debated and is not final. A White House spokesperson contacted by CNBC did not immediately respond to a request for comment.

British Prime Minister Theresa May has already expelled 23 Russians she said were spies after the poisoning of former spy Sergei Skripal and his daughter.

"The United States stands firmly with the United Kingdom in condemning Russia's outrageous action. The president is always considering options to hold Russia accountable in response to its malign activities. We have no announcements at this time," Deputy White House Press Secretary Raj Shah told Bloomberg on Saturday.

Trump — who as recently as this week has insisted on maintaining a cordial relationship with Russian President Vladimir Putin — is waiting to ensure other European allies will take similar steps against Russia before moving forward, the publication said.

Advisers to Trump met to discuss a U.S. response to the U.K. attack at a National Security council meeting on Wednesday, Bloomberg wrote.

Read more about Trump's plans for Russian diplomats on Bloomberg.