Los Angeles, California - The special counsel probing claims that Hunter Biden used his father's power and prestige to secure millions of dollars in bribes from a Ukrainian firm has charged a one-time FBI informant with lying, according to a federal indictment.

Alexander Smirnov (43) is accused of fabricating claims that President Joe Biden's son demanded the money to protect Burisma – on whose board he was serving at the time – from an investigation.

Smirnov's evidence has been touted by Republicans as proof that the Bidens were collectively involved in a criminal enterprise, which some in the party are using as justification for so-far unsuccessful attempts to impeach the current president.

A grand jury indictment filed in federal court in California on Wednesday says that for at least a decade Smirnov was acting as a "confidential human source (CHS)" for the FBI, providing his handler with information to be used in criminal investigations.

"Despite repeated admonishments that he must provide truthful information to the FBI and that he must not fabricate evidence, the Defendant provided false derogatory information to the FBI about" Joe and Hunter Biden, the filing says.

The indictment says in June 2020, Smirnov told his handler for the first time about meetings he claimed had taken place four or five years earlier in which executives from Burisma said they had hired Hunter Biden to "protect us, through his dad, from all kinds of problems."

He told the FBI the executives said "they had specifically paid $5 million each to" Joe and Hunter Biden so that Hunter would "take care of all those issues through his dad."

The document says this refers to a criminal investigation being conducted by the then-Ukrainian prosecutor general into Burisma.

"The events the Defendant first reported to the Handler in June 2020 were fabrications," the indictment says.

"The Defendant transformed his routine and unextraordinary business contacts with Burisma in 2017... into bribery allegations against (Joe Biden)... after expressing bias against (Biden) and his candidacy."

Smirnov, who is a US permanent resident, according to The New York Times, was arrested on Wednesday at an international airport in Las Vegas when he returned from overseas, the US Department of Justice said in a release on Thursday.

He faces one charge of making a false statement, and one of creating a false and fictitious record, in his dealings with an FBI investigation.

If convicted, he could be jailed for up to 25 years.

The claim that Hunter Biden leveraged his father's name for personal gain is central to a Republican narrative – pushed heavily by Donald Trump – that Joe Biden is corrupt.

The president's troubled son is a favorite target for conservatives, with outlets like Fox News repeatedly airing salacious details of his past as a drug addict.

They are using the allegations to underpin an impeachment investigation into the president, which has virtually no chance of ending in a conviction.

But it is being used as a platform to inflict damage on Biden ahead of the November presidential election – and a distraction from Donald Trump's multiple criminal and civil charges, which include an alleged conspiracy to overthrow the 2020 election.

Hunter Biden appeared in a federal court in Los Angeles last month to deny tax evasion charges.