President-elect Joe Biden’s son Hunter said on Wednesday that he learnt from federal prosecutors that his tax affairs are under investigation.
The investigation by the Delaware US Attorney’s office was disclosed by the president-elect’s transition office.
"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 advisers," Hunter Biden said in a statement.
He has long been a target of President Donald Trump and his allies, who have accused him of profiting from his political connections.
Mr Trump and his supporters also raised unsubstantiated charges of corruption related to Hunter Biden’s work in Ukraine at the time his father was vice president and leading the Obama administration’s dealings with the Eastern European nation.
The disclosure of the federal investigation comes at an awkward moment for the incoming president, who is assembling his Cabinet.
His choice for attorney general could have oversight of the investigation into his son if it is continuing when Mr Biden is sworn in on January 20.
“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,” his transition team said.
Hunter Biden joined the board of Ukrainian energy company Burisma in 2014, sparking concerns about the perceptions of a conflict of interest given that his father was deeply involved in US policy toward Ukraine.
A Republican-led Senate investigation into the matter did not find any laws that were broken and the report did not identify any policies that were directly affected by Hunter Biden’s work.