President Donald Trump's son Donald Jr was subpoenaed to testify before the Senate Intelligence Committee as part of its probe into Russian election meddling. Picture: Reuters/Joshua Roberts

Washington - President Donald Trump's son Donald Jr was subpoenaed Wednesday to testify before the Senate Intelligence Committee as part of its probe into Russian election meddling, US media reported.

It was the first known legal summons issued by Congress to a member of the president's family to force testimony in the ongoing investigation, and comes after Special Counsel Robert Mueller declined to accuse Trump's 2016 campaign of criminal conspiracy to collude with the Russians.

The surprise subpoena was issued by a Republican-led committee, opening a new source of strain between the Congress and a White House battling the legislature's pressure on multiple points. 

It came one day after Republican Senate Majority Leader Mitch McConnell declared "case closed" for the Russia investigation. 

Donald Jr., 41, has testified voluntarily in private once to the committee, and was peppered with questions about a June 9, 2016 meeting in Trump Tower in New York that he and other senior Trump campaign officials had with a Russian lawyer offering dirt on Democratic presidential candidate Hillary Clinton.

He was also quizzed about direct communications he had with Julian Assange, the founder of WikiLeaks, which leaked damaging documents and communications stolen by Russians from Clinton's campaign.

Committee sources would not confirm the subpoena or what they want to discuss with the president's eldest son, who currently helps run the Trump Organization, the family's real estate empire, and helps his father re-election campaign.

Citing a person close to Donald Jr., the Wall Street Journal said he had offered to answer questions in writing from the committee, and planned to fight the subpoena which demands that he testify in person.

AFP