Washington DC – Long a target of US Republicans, President Joe Biden's embattled son Hunter held a rare press conference Wednesday to push back against allegations his father was involved in his often-scrutinized international business dealings.

"My father was not financially involved in my business," Hunter Biden (53) said outside the US Capitol as the House of Representatives prepared to vote on whether to open a formal impeachment inquiry against his 81-year-old father.

"Not as a practicing lawyer, not as a board member of (Ukrainian gas giant) Burisma, not in my partnership to Chinese private businessmen, not in my investments at home nor abroad."

Hunter Biden also enraged Republican lawmakers by refusing a subpoena to testify at a closed-door hearing with them on Wednesday, insisting he would only give answers at a public session.

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Republicans have long used the scandal-plagued younger Biden as a way of targeting the Democratic president himself, especially as Joe Biden faces a likely reelection battle against Republican former president Donald Trump.

They have alleged that Joe Biden benefited unduly from his son's business dealings, and vice versa, while serving as vice president to Barack Obama, in what they claim is a family influence peddling scheme.

But Republicans have yet to provide any solid evidence of corruption by the president, and an impeachment is highly unlikely to be approved by the Democratic-controlled senate.

Hunter Biden still lashed out at the "shameless" impeachment probe.

"There is no fairness or decency in what these Republicans are doing. They have lied over and over about every aspect of my personal and professional life," he said.

The House Oversight Committee said in response that it would initiate contempt of Congress proceedings against him.

President Biden has avoided going into details of his only surviving son's legal woes, but has long expressed his support for him as a father.

The White House said the elder Biden knew in advance about his son's remarks on Wednesday.

"The president was certainly familiar with what his son was going to say," Press Secretary Karine Jean-Pierre told reporters.

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"What you saw was from the heart from his son," she said, and added that the president was proud of his son as he tried to "rebuild his life."

That reflected what appeared to be a strategy for Hunter Biden to take an increasingly public role in deflecting the attacks on him and his father, after years of virtual silence.

"For six years I've been a target of the unrelenting Trump attack machine, shouting. 'Where's Hunter?' Well, here's my answer – I am here," he said.

The younger Biden faces federal charges for lying about his drug use when he purchased a gun, as well as avoiding paying taxes while spending millions on drugs and escorts.

His personal life, in which he long struggled with addiction, has become fodder for Republican attacks over the years, with one hard-right member showing naked pictures of him from a stolen laptop during one House hearing.

"They've ridiculed my struggle with addiction, they've belittled my recovery and they have tried to dehumanize me – all to embarrass and damage my father," he said.

His statement came less than a week after another public attack on US right-wingers, whom he accused in a podcast with electronic musician Moby of trying to "kill" him.

In his memoir Beautiful Things, published in 2021, Hunter Biden wrote about his struggle with alcohol and illegal drugs – his version of many seedy stories that had already been widely reported in the media and spread by the political opposition.

Tragedy has also stalked his life. His mother and sister died in a 1972 car crash in which he was badly injured, while his older brother Beau died from brain cancer in 2015, aged 46.

"During my battle with addiction, my parents were there for me," he said Wednesday. "They literally saved my life."