Among the 60 Russian diplomats expelled from the U.S. last month were alleged spies suspected of tracking compatriots who resettled in the U.S., prompting concerns they were preparing to target expatriates labeled as traitors or enemies of the Kremlin, officials told CNN.

The Trump administration in late March expelled the diplomats and ordered Russia's consulate in Seattle to close to punish Moscow for its alleged role in poisoning an ex-spy in Britain. Senior Trump officials said all 60 Russians were spies working under diplomatic cover, and the move was, in part, to send a message to Russia's leaders there was an "unacceptably high" number of Russian intelligence operatives in the U.S.

Ex-spy and double agent Sergei Skripal and his daughter Yulia were poisoned in England on March 4 in a hit that points to Russia. The U.K. blamed Moscow for the attack, but Russia denies responsibility.

Still, U.S. and U.K. officials say Russia appears emboldened to carry out assassinations in Western democracies, per CNN.

"The trail of mysterious deaths, all of which happened to people who possessed information that the Kremlin did not want made public, should not be ignored by Western countries on the assumption that they are safe from these extreme measures," Democrats on the Senate Foreign Relations Committee wrote in a report earlier this year.