Federal authorities are investigating phone calls between President Trump's National Security Adviser Michael Flynn and the Russian ambassador to the U.S. on the day more sanctions were announced against Russia.

According to a CNN report, routine American eavesdropping on Russian diplomats caught the phone calls. Some of the conversation may have raised enough concerns in the intelligence community to warrant an investigation. The Wall Street Journal reported on Sunday night that Flynn is being investigated by U.S. counterintelligence agents.

Both reports said there is no determination of wrongdoing on Flynn's part thus far.

The White House denied knowledge of an investigation or why an investigation would be taking place Sunday.

The phone calls between Flynn and Sergey Kislyak came under scrutiny this month after reports were published showing the two were in contact multiple times on Dec. 29. That was the day the Obama administration announced increased sanctions against Russia for running an influence campaign on the American election.

The Trump camp initially denied the phone calls took place on Dec. 29, saying Flynn and Kislyak spoke the day before about setting up a meeting between Trump and Russian President Vladimir Putin. Later on, the Trump team confirmed Flynn and Kislyak did speak on Dec. 29, but did not discuss the sanctions.

Reports indicate Flynn and Kislyak spoke five times on Dec. 29.