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.
The concerns have been heightened following the poisoning in the UK of a former Russian spy, Sergei Skripal, and his daughter, who is a Russian citizen. British and US officials have blamed Russian intelligence for the use of a nerve agent in the attempted poisoning.
As reported, Russian ex-spy Sergei Skripal, 66, and daughter Yulia Skripal, 33, remain critically ill in hospital, after they were found unconscious on a bench in the Wiltshire city on March 4. The UK government says they were poisoned with a nerve agent of a type developed by Russia called Novichok and PM Theresa May said she believed Moscow was "culpable."
UK expelled 23 Russian diplomats as part of a "full and robust" response – prompting Russia's Foreign Minister Sergei Lavrov to say it will "certainly" expel British diplomats in response.
On March 16, Nato Secretary General Jens Stoltenberg said the alliance had "no reason to doubt the findings and assessments by the British government" which suggested Russian responsibility. He said the "UK is not alone" and Nato allies gave "strong political support" to Britain, following a joint statement from the US, France and Germany backing Mrs May's government and a pledge of support from Australia.
British Foreign Minister Boris Johnson said that the U.K.'s government believes that it was likely Putin's decision to direct the use of a nerve agent on the streets of the U.K.
On March 26, U.S. President Donald Trump ordered the expulsion of 60 Russians from the United States, including 12 people identified as Russian intelligence officers who have been stationed at the United Nations in New York.
BBC earlier reported that the 33-year-old left Salisbury District Hospital on Monday and has been taken to a secure location.