WASHINGTON (BLOOMBERG) - Joe Biden said on Thursday (Dec 17) that he believed efforts to use his son as a political cudgel amounted to "foul play" amid a federal investigation into Hunter Biden's tax matters and Republican calls for a special counsel investigation into his foreign dealings.

"We have great confidence in our son," Mr Biden said in an interview with CBS late-night host Stephen Colbert. "I'm not concerned about any accusations that have been made against him, it's used to get me. I think it's kind of foul play but - look, it is what it is."

CBS News originally reported that Mr Biden had called the federal investigation itself "foul play".

But the Biden campaign denied that characterisation and released a fuller transcript of the exchange, saying the President-elect was describing broader efforts to politically exploit his son's business dealings.

"There has indisputably been 'foul play' of that exact kind," Biden spokesman Andrew Bates tweeted, referring to people who use Mr Hunter Biden as a "cudgel" against his father.

"Trump got himself impeached engaging in it."

The comments were some of Mr Biden's most extensive since the disclosure earlier this month of the investigation into his son's tax dealings.

The probes include one led by the Delaware US Attorney's office into whether Mr Hunter Biden violated tax laws, and another by the US Attorney for the Western District of Pennsylvania concerns his activities in Ukraine and potential money laundering, according to a person familiar with the matter who discussed the sensitive inquiry on condition of anonymity. At least one of the probes has been ongoing since 2018, a third person said.

But the effort has been clouded by President Donald Trump's precedent-shattering public demands for an inquiry into Mr Biden's son. As recently as Sunday (Dec 13), Mr Trump complained that Attorney General William Barr did not disclose the federal tax inquiry before Election Day.

Mr Trump, in a tweet earlier on Thursday, denied playing any role in decisions regarding the investigation.

Mr Barr announced on Monday (Dec 14) that he plans to resign before Christmas. He made the announcement shortly after Trump criticised him in an interview with Fox News and White House Press Secretary Kayleigh McEnany told the network the president was "frustrated" Mr Barr hadn't done more to highlight the Hunter Biden case to voters.

Republican lawmakers - including Senate Judiciary chairman Lindsey Graham of South Carolina - have also seized on the probe, calling for the appointment of a special counsel.

Mr Colbert asked Mr Biden about his relationship with Mr Graham, a long-time friend, in light of Mr Graham's support for Mr Trump's efforts to overturn the election results. "Lindsey's been a personal disappointment because I was a personal friend of his," Mr Biden said.

He also said he would reach out to Republicans - even those who attack him - "if it benefits the country".

The investigation into Mr Biden's Ukraine work began based on information provided by Mr Trump's personal lawyer, Mr Rudy Giuliani, spurring tensions between Justice Department officials over how credible the allegations were.

Mr Hunter Biden confirmed that the investigation into his taxes is continuing. It's wasn't clear if the Ukraine-related investigation is still ongoing.

US officials also have conducted a counterintelligence assessment related to Mr Hunter Biden's activities, the person said.

The Bidens have repeatedly insisted no wrongdoing was committed, and the President-elect on Thursday again voiced support for his son.

"As long as he's good, we're good," Mr Biden said.