WASHINGTON (Reuters) - Donald Trump Jr. is unlikely to comply with a U.S. Senate Intelligence Committee subpoena to testify about his contacts with Russia, two congressional sources said on Thursday as the president publicly defended his eldest son.

The sources said Trump Jr is expected to cite his Fifth Amendment constitutional right to avoid self-incrimination, a day after reports that the Republican-led panel had issued what is the first publicly known subpoena for a member of the president’s family.

Trump, who has blasted the investigations into him and Russia, defended his son, who runs the Trump Organization - a private business that the Republican president still owns.

“I was very surprised,” Trump said at a White House event intended to highlight healthcare. “My son’s a very good person. Works very hard.”

Lawyers for Trump Jr. did not respond to requests for comment and a White House spokesman declined to comment.

Discussions between the Republican-led panel and Trump Jr. about his possible testimony have been going on for months, according to the sources, who asked not to be named given the panel’s ongoing probe.

Lawmakers on the Republican-led committee, which is among several congressional panels investigating Russian interference in the 2016 U.S. election, want to question Trump Jr. about his contacts with Moscow.

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Trump Jr. had appeared before the panel previously to answer questions from committee staff, according to congressional sources. The subpoena was issued now because Senators want to question him themselves, they said.

The sources said the senators want to question Trump Jr. about testimony he gave to the Senate Judiciary Committee in September 2017 which was subsequently contradicted by Michael Cohen, Trump’s former lawyer who started his prison sentence this week in part for lying to Congress.

Led by Republican chairman Richard Burr, the intelligence panel is the only committee in the Republican-controlled Senate that has been conducting a bipartisan investigation into allegations of Russian interference in U.S. politics.

The reported subpoena prompted sharp rebukes from some of Trump’s staunchest defenders within the party as Republicans sought to move on from a two-year investigation by U.S. Special Counsel Robert Mueller, whose findings were released in part last month.

Mueller’s team of prosecutors said there was a “reasonable argument” that Trump Jr. had violated campaign finance laws but concluded they did not believe they could obtain a conviction.

On Tuesday, Senate Majority Leader Mitch McConnell took to the Senate floor with a speech seeking to close the door on the investigations, declaring “case closed.”

It was not immediately clear when the panel issued the subpoena, which was first reported by Axios on Wednesday.

In resisting the congressional subpoenas, Trump Jr. joins several Trump administration officials who are refusing to cooperate with congressional subpoenas, including Attorney General William Barr and former White House lawyer Don McGahn.

The Trump administration is also refusing to turn over copies of the president’s personal and business tax documents requested by House Democrats.