WASHINGTON: Congressional Republicans lodged a formal case Monday for the impeachment of US President Joe Biden, using the opening day of the Democratic National Convention (DNC) to launch a political assault unlikely to gain serious traction.

The report from three powerful committees in the Republican-led House of Representatives accuses Biden of corruption linked to his son Hunter's foreign business affairs.

Jim Jordan, head of the Judiciary committee, said the probe showed "conclusively" that Biden had "abused his public office for the private financial benefit of the Biden family and Biden business associates". 

However, Republicans have not provided any direct proof that Biden ever used his office to benefit his son or was involved in Hunter's businesses.

There was no smoking gun in a document built around inferences and innuendo about connections between father and son, with many of the accusations related to the period when Biden was out of office, after serving as Barack Obama's vice president.

Biden — set to deliver a swan song speech at the Democratic convention and pass the political torch to his vice president Kamala Harris — has repeatedly denied helping his son's business ventures, including in Ukraine and China.

Republicans have for years used Hunter Biden's foreign links and chaotic personal life as a recovering drug addict to try and embarrass the president.

However, marathon attempts to build an impeachment case against Biden — seen by many as a bid for revenge over the two impeachments of Republican Donald Trump when he was president — have never come close to an actual vote by the House.

Republicans hold only a razor-thin majority and it remains unclear whether Monday's report will ever lead to a formal vote on impeaching Biden as the party would require near unanimity to overcome Democratic opposition.

If the House did impeach Biden, the Democratic-controlled Senate would be sure to acquit the president.

The Democratic side on the House Oversight and Accountability Committee dismissed the Republican effort, saying the case had no substance, despite a "mountain" of documentation.

The "mountain of evidence definitively proves that Biden did not commit any wrongdoing, let alone any high crime, misdemeanor, or other impeachable offence," the Democrats said in a statement.