The lawyer for embattled former national security adviser Michael Flynn said Flynn won't comply with a Senate Intelligence Committee subpoena, according to the committee's top Republican.

Senate Intelligence Committee Chairman Richard Burr and Vice Chairman Mark Warner are determining how to proceed after Flynn has not agreed to comply with their May 10 subpoena for documents about his interactions with Russian officials.

Flynn was ousted in February for misleading Vice President Mike Pence about his contacts with the Russian ambassador. He has been under investigation by the FBI for secretly working as a paid lobbyist for Turkey during the presidential campaign, a fact he disclosed to the White House weeks before Mr. Trump's inauguration, according to a Wednesday New York Times report. President Trump brought him on anyway.

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In February, the day after Flynn was ousted, the president asked now-fired FBI director James Comey to drop an FBI investigation into Flynn. That revelation came Tuesday, reports of a memo Comey wrote right after the February meeting.

On Wednesday night, Deputy Attorney General Rod Rosenstein announced he had appointed former FBI director Robert Mueller to be the special counsel in charge of the FBI's ongoing investigation into Russian election meddling and any ties between Russia and the Trump campaign.

Flynn's lawyer, Robert Kelner, had already told the panel he would not voluntarily provide the documents responsive to an earlier April 28 request.

White House Press Secretary Sean Spicer has blamed the Obama administration for not sufficiently vetting Flynn, pointing out that Flynn had a security clearance under the previous president.

CBS News' Alan He contributed to this report.