Washington (CNN) Among the dozens of Russian diplomats the US expelled last month were suspected spies who US law enforcement and intelligence officials believe were tracking Russian defectors and their families who had resettled in the US, officials briefed on the matter tell CNN.

In at least one instance, suspected Russian spies were believed to be casing someone who was part of a CIA program that provided new identities to protect resettled Russians, the officials said.

That episode and other US intelligence raised concerns that the Russians were preparing to target Russian émigrés in the US labeled by the Kremlin as traitors or enemies, law enforcement and intelligence officials said.

The CIA declined to comment. The White House declined to comment.

The Russian embassy did not respond to a request for comment.