(CNN) US investigators are scrutinizing late December calls between Mike Flynn, President Donald Trump's national security adviser, and Russia's ambassador to the US as part of a broader counterintelligence investigation of Russian activities in the US, law enforcement and intelligence officials told CNN.

The calls were captured by routine US eavesdropping targeting the Russian diplomats, according to the intelligence and law enforcement officials. But the officials said some of the content of the conversation raised enough potential concerns that investigators are still looking into the discussions, amid a broader concern about Russian intelligence-gathering activities in the United States.

The officials all stressed that so far there has been no determination of any wrongdoing.

FBI and intelligence officials briefed members of the Obama White House team before President Barack Obama left office about the Flynn calls to the Russian ambassador, sources said.

At a press briefing Monday, Trump press secretary Sean Spicer said he had discussed the issue with Flynn on Sunday. Spicer said there had been two calls between Flynn and the Russian ambassador and that they covered only four subjects: Setting up a call between Trump and Russian President Vladimir Putin; exchanging holiday greetings; offering condolences for lives lost in a Russian plane crash; and a Syria conference on ISIS.

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