A top congressional committee yesterday issued a subpoena for former national security advisor Michael Flynn, seeking documents in its investigation into links between the Trump campaign and Russia.

Senate Intelligence Committee chairman Richard Burr and ranking member Mark Warner said the step was taken after Flynn rejected their April 28 request to provide information on his contacts with Russian officials and businessmen.

"The subpoena requests documents relevant to the Committee's investigation into Russian interference with the 2016 election," Burr and Warner said.

In a simultaneous development, it appears that FBI director, James Comey, days before Trump fired him, had sought more resources for his probe into possible collusion between Trump's campaign and Russia.