Hunter Biden has been indicted on federal firearms charges, the latest and weightiest step yet in a long-running investigation into the US president’s son.

Biden is accused of lying about his drug use when he bought a firearm in October 2018, a period when he has acknowledged struggling with addiction to crack cocaine, according to the indictment filed in federal court in Delaware.

President Joe Biden’s son has also been under investigation for his business dealings.

The special counsel overseeing the case has indicated that charges of failure to pay taxes on time could be filed in Washington or in California, where he lives.

President Joe Biden and his son Hunter Biden
Hunter Biden with his father Joe Biden (Andrew Harnik/AP)

The indictment comes as congressional Republicans pursue an impeachment inquiry into the Democratic president, in large part over Hunter Biden’s business dealings.

Republicans have obtained testimony about how Hunter Biden used the “Biden brand” to drum up work overseas, but they have not produced hard evidence of wrongdoing by the president.

The three-count indictment alleges Hunter Biden lied on a form required for every gun purchase when he bought a Colt Cobra Special at a Wilmington, Delaware, gun shop in October 2018.

He is charged with two counts of making false statements by checking a box falsely saying he was not a user of or addicted to drugs and of illegally possessing the gun as a drug user and a third count for possessing the gun as a drug user.

Two counts are punishable by up to 10 years in prison while the third carries up to five years in prison, upon conviction.

A felony gun charge against Hunter Biden, 53, had previously been part of a plea deal that also included guilty pleas to misdemeanor tax charges, but the agreement imploded during a court hearing in July when a judge raised questions about its unusual provisions.

Defence lawyers have argued that a part of the deal sparing Hunter Biden prosecution on the gun count if he stays out of trouble remains in place.

It includes immunity provisions against other potential charges.

Lawyers indicated they would fight additional charges filed against him, but did not immediately respond to a request for comment on Thursday.

Prosecutors, though, maintain the agreement never took effect and is now invalid.

They telegraphed charges were coming earlier this month.

Charges related to gun possession by drug users are rare, especially when not in connection with other crimes.

Of all the people sentenced for illegal gun possession in 2021, about 5% were charged due to drug use, according to US Sentencing Commission data.

A federal appeals court, meanwhile, recently found a longstanding ban did not stand up to new standards for gun laws set by the Supreme Court.

Republicans had denounced the plea agreement as a “sweetheart deal”.

It would have allowed Hunter Biden to serve probation rather than jail time after pleading guilty to failing to pay taxes in both 2017 and 2018.

His personal income during those two years totalled roughly four million dollars (£3.2 million), including business and consulting fees from a company he formed with the chief executive of a Chinese business conglomerate and the Ukrainian energy company Burisma, prosecutors have said.

Congressional Republicans have continued their own investigations into the Justice Department’s handling of the case as well as nearly every aspect of Hunter Biden’s business dealings, seeking to connect his financial affairs directly to his father.

They have failed to produce evidence that the president directly participated in his son’s work, though he sometimes had dinner with his son’s clients or said hello to them on calls.