Former National Security Advisor Mike Flynn has told the Senate Intelligence Committee he is willing to testify about the Trump campaign's possible ties to Russia in return for immunity from prosecution, a Congressional official told NBC News.

The Wall Street Journal reported Thursday that Flynn had told the FBI and Congress he was willing to be interviewed in exchange for a grant.

More from NBC News:

Michael Flynn Resigns as National Security Adviser Over Talks With Russia

Russians Paid Mike Flynn $45K for Moscow Speech, Documents Show

Official: Flynn Discussed Sanctions With Russians Before Taking Office

Flynn, a retired Lt. Gen. who headed the Defense Intelligence Agency before being pushed out by the Obama administration, advised the Trump campaign beginning in 2015. He served as President Trump's national security advisor for three weeks before resigning for what the Trump administration said was misleading Vice President Mike Pence about his contacts with Russian Ambassador to the U.S. Sergey Kislyak.

Tweet on Flynn counsel statement

Flynn was paid $45,000 plus expenses to speak at the 10th anniversary gala of the RT television network in Moscow in December 2015, while he was already an advisor to Trump. The U.S. considers RT, which is state-sponsored, to be a propaganda outlet.

Prior to Trump's inauguration, on the day that President Obama announced sanctions against Russia as punishment for interfering in the U.S. election, Flynn spoke on the phone with Russian Ambassador Kislyak.

A U.S. intelligence official told NBC News that Flynn had discussed the hacking-related sanctions with Kislyak prior to Trump's inauguration. Flynn told the Washington Post he didn't discuss sanctions with Kislyak, then said he couldn't remember whether they had discussed sanctions.

Watch: WH officials briefed Nunes, Flynn agrees to testify for immunity