US investigators are scrutinizing late December calls between Mike Flynn, Donald Trump's national security adviser, and the Russian ambassador to the US as part of a counterintelligence investigation of Russian activities in the United States.

The calls were captured by US eavesdropping targeting the Russian diplomats. US officials declared some of the content of the conversation raised concerns about Russian intelligence-gathering activities in United States.The officials stressed that so far there has been no determination of any wrongdoing. 

FBI and intelligence officials briefed members of the Obama team before President Obama left office about the Flynn calls to the Russian ambassador.

Calls were related with four subjects

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

The calls were heard in the course of monitoring of communications of Russian diplomats. US intelligence agencies routinely capture communications of senior foreign officials, including those based in the US. The Wall Street Journal was first to report that investigators had looked at the calls. 

Among the communications being scrutinized are calls between Flynn ans Russia's ambassador, Sergey Kislyak on December 29.

US sanctions against Russia

The calls came on the same day that United States announced more sanctions against Russia and expelled a group of 35 Russian diplomats. A Trump official told CNN on January 16th that Kislyak and Flynn did not discuss the Russian sanctions. On the same day, multiple Trump officials declared the call focused on the logistics of connecting Trump and Russian President Vladimir Putin after the inauguration for a phone conversation.