The US House of Representatives has voted to formally authorise its ongoing impeachment inquiry into President Joe Biden, as Republicans unite behind the effort even though they have yet to find evidence of wrongdoing by the Democrat.
The Republican-controlled chamber voted 221-212 along party lines to approve the probe, which is examining whether Biden improperly benefited from his 53-year-old son Hunter Biden's foreign business dealings, hours after the younger Biden refused a call to testify behind closed doors.
The White House has dismissed the inquiry as unsubstantiated by facts and politically motivated.
Biden in a statement chastised House Republicans for not acting on his request for any of his domestic priorities or providing emergency funding for Ukraine and Israel.
"House Republicans are not joining me. Instead of doing anything to help make Americans' lives better, they are focused on attacking me with lies," Biden said.
Biden is preparing for a possible 2024 election rematch with his Republican predecessor, Donald Trump.
Trump is the first president in US history to be impeached twice and is currently preparing for four upcoming criminal trials.
The effort will almost certainly fail to remove Biden from office.
Even if the House votes to impeach the president, the Senate would then have to vote to convict him by a two-thirds vote - a near impossibility when Biden's fellow Democrats hold a 51-49 majority.
But it could help Republicans highlight their allegations of corruption through much of the 2024 campaign.
The vote comes three months after Republicans informally began the probe and is not a required step to remove a president or other official from office.
However, authorisation could give Republicans more legal authority to force Biden's administration to co-operate and could help to counter accusations from Democrats who say it lacks legitimacy.
House Republicans allege Biden and his family profited from his actions when he served as Barack Obama's vice-president from 2009 to 2017, and they have zeroed in on his son's business ventures in Ukraine and China during that period.
They have turned up evidence that the younger Biden led clients to believe that he could provide access to the vice-president's office, but they have not provided evidence that Biden took any official actions to help those businesses or benefited financially from them.
"By endorsing this impeachment inquiry, the Republican Conference is signing up for another year of a 'do nothing' Congress: no substantive legislation or policy progress, all political fantasy and conspiracy theory," said Democratic representative Jamie Raskin in a statement.
Earlier, Hunter Biden defied a committee subpoena to testify behind closed doors, saying he would testify only in public as he feared his words would otherwise be misrepresented.
"There is no evidence to support the allegations that my father was financially involved in my business, because it did not happen," Hunter Biden said.
Members of the committee said they would take steps to hold him in contempt of Congress, which could potentially result in prison time.
"As President Biden continues to stonewall lawful congressional subpoenas, today’s vote of the full House of Representatives authorising the inquiry puts us in the strongest position to enforce these subpoenas in court," Republican House Speaker Mike Johnson posted on social media.
Trump, the frontrunner for the Republican presidential nomination, was impeached twice by the House during his presidency: in 2020 for trying to pressure Ukraine to announce a corruption investigation of Biden, and in 2021 for trying to overturn his election loss.
Both attempts foundered in the Senate.
Hunter Biden, who has described his struggles with drug and alcohol addiction, has also been the subject of a years-long criminal investigation.
He faces federal charges that he lied about his drug use while buying a handgun and separate charges of failing to pay $US1.4 million ($A2.1 million) in taxes.
He has pleaded not guilty to the gun charges, and his lawyer says he has repaid his taxes in full.
"In the depths of my addiction, I was extremely irresponsible with my finances. But to suggest that is grounds for an impeachment inquiry is beyond the absurd. It's shameless," he said.