U.S. counterintelligence agents have investigated communications between Russian officials and President Donald Trump's national security adviser, Michael Flynn.
Flynn came under scrutiny earlier this month after reports surfaced that he had phoned the Russian ambassador to the U.S. on the same day President Obama expelled 35 Russian diplomats in response to the Kremlin's reported election hacking.
The FBI, CIA, National Security Agency, and Treasury Department have all launched investigations into Flynn's Russian contacts in an attempt to determine the extent of overlap between Moscow and Trump aides, the Wall Street Journal reported, citing unnamed officials.
It is unclear when the probe began or whether it uncovered noteworthy evidence.
The investigation focused primarily on Flynn's contact with Russian Ambassador Sergey Kislyak on Dec. 29. The Obama administration had announced that day it was blacklisting top officials in the Russian security services and imposing additional sanctions.
Counterintelligence officials also probed earlier communications between Flynn and Russian officials.
White House spokeswoman Sarah Sanders said in a statement Sunday night the administration has "absolutely no knowledge of any investigation or even a basis for such an investigation."
Flynn, a retired lieutenant general who served as a military adviser to Trump during the campaign, will have a crucial role in shaping U.S. policy toward Russia.
He has been accused of being too close to the Kremlin. Flynn once appeared on Kremlin propaganda network RT and received a speaking fee from the outlet. Flynn shared a dinner table with Putin after he spoke at an RT gala.