US President-elect Joe Biden’s son Hunter Biden says his tax affairs are under federal investigation, reigniting questions about his financial dealings that clouded his father’s election campaign.

“I take this matter very seriously but I am confident that a professional and objective review of these matters will demonstrate that I handled my affairs legally and appropriately, including with the benefit of professional tax advisors,” Hunter Biden said on Wednesday (US time).

He said he learned of the investigation for the first time on Tuesday, when prosecutors informed his lawyer of the probe.

The Biden transition team on Wednesday released a statement saying, “President-elect Biden is deeply proud of his son, who has fought through difficult challenges, including the vicious personal attacks of recent months, only to emerge stronger.”

CNN reported investigators have been examining multiple financial issues, including whether Hunter Biden and his associates violated tax and money laundering laws in business dealings in foreign countries, principally China, according to two people briefed on the probe.

The investigation began as early as 2018, predating the arrival of William Barr as US attorney-general, sources told CNN.

The US Attorney’s Office declined to comment.

Hunter Biden became a focus of attacks from President Donald Trump and his Republican allies in the campaign for the White House.

They have questioned potential conflicts of interest from his position on the board of a Ukrainian energy company at the time Joe Biden was the US vice-president.

Mr Trump’s actions in connection with the Ukrainian matter led to his impeachment by the House of Representatives last January.

Mr Trump also called during the campaign for China to investigate the involvement of Mr Biden’s son in a fund that sought to raise Chinese capital.

Mr Trump accused the younger Biden of using his position of influence to secure China’s financial backing for his investments.

Mr Trump never provided evidence to support this claim and Hunter Biden has repeatedly denied wrongdoing.