Washington (AFP) - President Donald Trump's eldest son will testify Wednesday behind closed doors to a Republican-led Senate committee investigating Russia election meddling, a congressional source said.

The appearance by Donald Trump Jr before the Senate Intelligence Committee follows a dispute that made headlines last month when the president expressed surprise that his son was being hauled before Congress for a second time as part of the panel's probe.

Trump Jr, the 41-year-old currently at the helm of the Trump Organization, is expected to be questioned beginning around 9:15 am (1315 GMT), the source familiar with the proceedings said Tuesday.

The panel's chairman, Republican Senator Richard Burr, faced criticism from within his own party for calling Trump Jr to appear a second time, due to apparent discrepancies between his original 2017 testimony and that of other witnesses.

This time, the panel, which is known for its bipartisanship, wants to revisit some of Trump Jr's earlier statements, including about a proposed Trump Tower project in Moscow, according to US media.

Some Democrats suspect he may have lied about what he and his father knew about a June 2016 meeting in Trump Tower with a Russian lawyer offering dirt on Democratic nominee Hillary Clinton, as well as other connections between the two sides.

Trump Jr had initially agreed to testify voluntarily twice before postponing, leading to the panel's subpoena issued in April.

He and the committee's leaders eventually reached an agreement limiting the number of questions in the session, which is expected to last a maximum of four hours, according to the Washington Post.

For two years, the committee's Republicans and Democrats have been quietly investigating Russian interference in the US presidential election of 2016.

President Trump is battling any cooperation with Congress in the Russia meddling investigation, claiming that he has already been "totally exonerated" of collusion and obstruction of justice by special prosecutor Robert Mueller's report, which was completed in late March.

The report did not find any clear evidence to charge members of Trump's campaign with conspiring with Russia, but neither did it exonerate the president of obstruction of justice.

Rather, Mueller outlined 10 instances of potential obstruction that he uncovered during the probe.