US prosecutors say in a court filing they will seek an indictment of President Joe Biden's son Hunter by September 29 in his tax and firearms case.
David Weiss, who was appointed special counsel by US Attorney General Merrick Garland in August, said in a court filing that the government would seek a grand jury indictment before the September 29 deadline under the Speedy Trial Act.
A lawyer for Hunter Biden did not immediately respond to a request for comment.
"The government intends to seek the return of an indictment in this case before that date," Weiss wrote in a status report to US District Judge Maryellen Noreika.
In July, Noreika rejected a proposed plea deal that would have resolved the tax and gun charges, raising concerns over its legality and the scope of immunity it offered Hunter Biden.
Hunter Biden's lawyers said in court filings last month that prosecutors reneged on a plea deal that would have resolved the charges, raising the possibility of a criminal trial as the 2024 presidential election approaches.
Under that proposed plea arrangement, Hunter Biden would have pleaded guilty to not paying taxes on $US1.5 million ($A2.3 million) in income between 2017 and 2018 and entered into a separate deferred prosecution agreement for illegally owning a firearm while using drugs - a felony.
The case has become a political lightning rod.
Republicans in Congress have raised the possibility of impeaching Biden over his son's business dealings and accuse the Department of Justice of giving him a "sweetheart deal".
Garland has denied Republican accusations of favouritism and elevated Weiss from US Attorney for the District of Delaware who has been investigating the case since 2019.
As special counsel, Weiss, an appointee of former president Donald Trump, has additional authority.
If the case goes to trial, the president would be campaigning for re-election in November 2024, likely against Trump, as his son faces criminal prosecution.
Trump, a Republican, faces at least three criminal trials of his own next year.