The officials say they believe one of the biggest U.S. adversaries feels emboldened by the lack of a significant retaliatory response from both the Trump and Obama administrations, CNN wrote.
"Russians have maintained an aggressive collection posture in the U.S., and their success in election meddling has not deterred them," said a former senior intelligence official familiar with Trump administration efforts.
Russians could also be seeking more information on Trump's administration, which is new and still unpredictable to Moscow, according to Steve Hall, retired CIA chief of operations.
Read alsoCIA chief Pompeo on MSNBC: Russians trying to undermine American democracy for decades"Whenever there is a deterioration of relations between countries – the espionage and intelligence collection part becomes that much more important as they try to determine the plans and intentions of the adversarial government," Hall said.
Since the November election, U.S. intelligence and law enforcement agencies have detected an increase in suspected Russian intelligence officers entering the U.S. under the guise of other business, according to multiple current and former senior U.S. intelligence officials. The Russians are believed to now have nearly 150 suspected intelligence operatives in the U.S., these sources said. Officials who spoke to CNN say the Russians are replenishing their ranks after the U.S. in December expelled 35 Russian diplomats suspected of spying in retaliation for election-meddling.