In America, federal prosecutors have been investigating Hunter Biden, the son of US President-elect Joe Biden, to decide if according to individuals familiar with the matter and a statement from Hunter Biden, he neglected to disclose revenue from China-related business transactions.

The announcement is bound to result in a politically explosive investigation that is sure to threaten the new administration's Justice Department.

The inquiry into the son of Mr. Biden started in 2018, but nothing could be immediately learned about what, if any, misconduct he had uncovered.

In a statement saying he had just been informed of it the investigation was confirmed by Hunter Biden.

FBI agents were trying to speak to Hunter Biden as part of the case on Tuesday, according to a person familiar with the matter, but an interview has not yet been arranged or taken place, as well as serving subpoenas on Hunter Biden and his associates.

"I learned for the first time yesterday that the US Delaware attorney's office advised my lawyer yesterday, too, that they are investigating my tax affairs," Hunter Biden said in a tweet.

"I take this matter very seriously, but I am confident that a professional and objective review of these issues will show that I have handled my affairs legally and properly, including for the benefit of professional tax consultants."

The counsel for Hunter Biden, George Mesires, did not respond to requests for more information on the case.

The Biden transition team wrote in a statement that "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."

While the investigation has been underway for some time, it is unknown how far prosecutors are considering building or closing a criminal case.

Usually, interviewing the target of an inquiry happens when investigators have gathered a lot of facts, while prosecutors attempting to serve subpoenas as recently as this week imply that more investigative work needs to be done.

The inquiry continued throughout the election year a person familiar with the case said but agents took precautions not to take explicit investigative action as voting neared, which would have made it more widely known. When the election was over, those precautions, the individual said, were unnecessary.

This will represent a big test for him and his attorney general if the investigation continues as Joe Biden takes office.

During the Trump administration, Democrats blamed the Justice Department for sacrificing its historic independence from the White House, as Attorney General William Barr interfered in proceedings for the benefit of friends of Donald Trump, and Joe Biden's new chief of staff said the president-elect would not tell the Department of Justice who to prosecute.

Mr. Biden has not yet selected a candidate to head the Department of Justice, and it is possible that whoever he selects will be urged to make public promises on how they will oversee the President's son's investigation.

The international business ventures of Hunter Biden have long dogged the political life of his father, as Republicans have argued that they provided his father with conflicts of interest.

Throughout the presidential campaign, Mr. Trump and his GOP allies attacked Hunter Biden, particularly his work for a Ukrainian gas company while his father was vice-president, as well as his business affairs related to China.

Mr. Trump invited Hunter Biden's former business associate to attend the final presidential debate, and the associate addressed an arrangement involving a Chinese corporation in a staged event beforehand.

Tony Bobulinski, the associate, alleged that he met Joe Biden and his son and Joe Biden's brother Jim in May 2017 to discuss a joint venture with the Chinese energy company CEFC.

That was after Joe Biden quit public office, and in 2020, it was far from clear that he would run again. But Bobulinski seemed to deny the claim by Joe Biden that he had never addressed his son's international business dealings.