FILE PHOTO: Then White House National Security Advisor Michael Flynn walks down the White House colonnade on the way to Japanese Prime Minister Shinzo Abe and U.S. President Donald Trump's joint news conference at the White House in Washington, U.S., February 10, 2017. REUTERS/Jim Bourg/Files

(Reuters) - Relatives of former national security adviser Michael Flynn have set up a fund to help pay for his legal defense against federal and congressional investigations into potential collusion between Donald Trump’s presidential campaign and Russia.

The fund was established by Flynn’s brother Joe and sister Barbara Redgate, who said in a statement the “enormous expense” of legal fees had put a “tremendous financial burden on our brother Mike and his family.”

They asked supporters of the retired U.S. general, “veterans, and all people of goodwill” to contribute to the fund, which will collect donations from U.S. citizens through a newly created website, according to the statement.

Flynn, a central figure in a federal probe led by special counsel Robert Mueller, as well as a focal point of congressional investigations, broke a months-long silence to thank his siblings for their support on Twitter.

“Lori and I are very grateful to my brother Joe and sister Barbara for creating a fund to help pay my legal defense costs,” Flynn said in a tweet, referring to his wife Lori.

Flynn was fired by Trump as national security adviser after less than a month on the job. The firing came 18 days after a senior Justice Department official warned that Flynn could be blackmailed because Moscow knew he made misleading statements about his contacts with Russian officials.

Flynn in August reported income of at least $1.8 million, according to an amended financial disclosure form, which included paid speaking engagements to Russian entities, including the Kremlin-funded RT TV and Volga-Dnepr Airlines and payments for lobbying for the Turkish government.

Investigators are looking at whether payments from foreign clients to Flynn and his company, the now-inactive Flynn Intel Group, were lawful, sources have told Reuters.