(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.

The-CNN-Wire ™ & © 2017 Cable News Network, Inc., a Time Warner Company. All rights reserved. (photo: CNN)