The Wall Street Journal is reporting that United States counterintelligence officials are investigating Donald Trump national security adviser Michael Flynn’s phone calls with Russia, according to people familiar with the matter.

REPORT: US intelligence agents investigating Flynn calls with Russia

The WSJ report follows up on an earlier Associated Press report that confirmed that Michael Flynn had contact with the Russian ambassador – a possible violation of the Logan Act –  on the same day that President Obama was announcing sanctions against Russia for their interference in the 2016 election.

According to the Wall Street Journal report:

The counterintelligence inquiry aimed to determine the nature of Mr. Flynn’s contact with Russian officials and whether such contacts may have violated laws, people familiar with the matter said.

A key issue in the investigation is a series of telephone calls Mr. Flynn made to Sergey Kislyak, the Russian ambassador to the U.S., on Dec. 29. That day, the Obama administration announced sanctions and other measures against Russia in retaliation for its alleged use of cyberattacks to interfere with the 2016 U.S. election. U.S. intelligence officials have said Russian President Vladimir Putin ordered the hacks on Democratic Party officials to try to harm Hillary Clinton’s presidential bid.

Evidence of coordination mounting

U.S. counterintelligence officials have collected evidence showing repeated contacts between Flynn and Kislyak according to the Wall Street Journal sources these people said. “It is common for American officials’ conversations with foreign officials to surface in NSA intercepts, because the U.S. conducts wide-ranging surveillance on foreign officials. American names also may surface in descriptions of conversations shared among officials of foreign governments,” the Wall Street Journal piece went on to say.

Additionally, the Senate Intelligence Committee is also investigating the possibility of coordination and collusion between Russia and Donald Trump’s campaign as part of their broader investigation into Russian election interference.