Russian spies are ramping up their intelligence-gathering efforts in the US, according to current and former US intelligence officials, who say they have noticed an increase since the presidential election.

The officials say they believe one of the biggest US adversaries feels emboldened by the lack of a significant retaliatory response from both the Trump and (former US President) Barack Obama administrations, CNN reported on Thursday.

“Russians have maintained an aggressive collection posture in the US, 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.

“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, US intelligence and law enforcement agencies have detected an increase in suspected Russian intelligence officers entering the US under the guise of other business, according to multiple current and former senior US intelligence officials.

The Russians are believed to now have nearly 150 suspected intelligence operatives in the US, these sources said. Officials who spoke to CNN say the Russians are replenishing their ranks after the US in December expelled 35 Russian diplomats suspected of spying in retaliation for election-meddling.

“The concerning point with Russia is the volume of people that are coming to the US. They have a lot more intelligence officers in the US” compared to what they have in other countries, one of the former intelligence officials says.

The FBI, which is responsible for counterintelligence efforts in the US, would not comment for the story.

Fueling law enforcement officials’ concern is that the Russians are targeting people in the US who can provide access to classified information, in addition to ongoing efforts to hack the US government for intelligence, according to several of the officials.

In some cases, Russian spies have tried to gain employment at places with sensitive information as part of their intelligence-gathering efforts, the sources say.