(Reuters) - The U.S. Senate Intelligence Committee has asked the son of President Donald Trump’s former national security adviser to provide documents and testimony as part of the panel’s probe into Russian meddling in the 2016 U.S. election, a source familiar with the congressional matter told Reuters.

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Michael G. Flynn was a close aide to his father, former U.S. Army general Michael Flynn, 58, who was fired by Trump three weeks into his White House job in February as he came under scrutiny for his foreign contacts.

The son managed his father’s schedule and accompanied him on trips while working at Flynn Intel Group consultancy, including one to Moscow in 2015 for an event where the elder Flynn sat next to Russian President Vladimir Putin. Russia has repeatedly denied the conclusions of U.S. intelligence agencies that Moscow interfered in the presidential campaign to help Republican Trump by hacking Democratic Party emails and spreading propaganda online.

Barry Coburn, a lawyer for the younger Flynn, 34, declined to comment on the Senate committee’s request, which was reported earlier by NBC News. The panel could issue a subpoena to the younger Flynn, although he could invoke his Fifth Amendment constitutional protection against self-incrimination and not comply.

The elder Flynn has also been asked by the panel to provide information and to testify. A source close to Flynn said that he had turned over documents to intelligence committees in both the Senate and U.S. House of Representatives.

The source familiar with the congressional investigation said that the Senate committee is not satisfied and wants to obtain more evidence from him.

The source also confirmed that the Senate panel was issuing a subpoena to former Trump campaign foreign policy adviser Carter Page after Page declined committee requests that he voluntarily turn over records related to any contacts with Russians.

Page told Reuters in an email on Tuesday that he was “cooperating with everyone in D.C. who might want my help in the interest of helping our country get to the end of this witch hunt.” Page has said it was touched off by the circulation of a dossier produced by former British spy Christopher Steele on purported links between Trump, his advisers and Russia.

The Senate committee, which has sought to speak with Steele, is also investigating whether there was any collusion between then-candidate Trump’s campaign and Moscow officials. Trump has denied any collusion by his associates, calling it “fake news.”

The Flynn consultancy’s business activities are under scrutiny by congressional and federal investigators mainly because of the lobbying work it did for a Turkish businessman.

Various congressional panels are sparring over Steele’s reports outlining Russian financial and personal links to Trump’s campaign and associates.