WASHINGTON (Reuters) – Former White House National Security Adviser Michael Flynn will decline to comply with a subpoena from the Senate Intelligence Committee investigating possible Russian interference in the 2016 U.S. election, according to media reports on Monday.

Flynn will invoke his Fifth Amendment protection against self-incrimination, the Associated Press, Wall Street Journal and Fox News reported, citing sources close to Flynn.

The retired lieutenant general, a key witness in the Russia probe, planned to inform the panel of his decision later on Monday, the reports said.

The Senate Intelligence Committee is conducting one of the main congressional probes of alleged Russian meddling in the U.S. presidential election and whether there was any collusion between President Donald Trump’s campaign and Russia.

The committee first requested documents from Flynn in an April 28 letter, but he declined to cooperate with the request.

The U.S. intelligence community concluded in January that Moscow tried to sway the November vote in Trump’s favor. Russia has denied involvement and Trump insists he won fair and square.

Flynn was forced to resign in February, after less than a month on the job, for failing to disclose the content of his talks with Sergei Kislyak, Russia’s ambassador to the United States, and then misleading Vice President Mike Pence about the conversations.

Reuters reported on Thursday that Flynn and other advisers to Trump’s campaign were in contact with Russian officials and others with Kremlin ties in at least 18 calls and emails during the last seven months of the U.S. presidential race. Flynn has acknowledged being a paid consultant to the Turkish government during the campaign.

(Reporting by Doina Chiacu Editing by W Simon and Dan Grebler)