Prosecutors in the US criminal tax case against Hunter Biden accused him of accepting payments from a Romanian businessman who sought to "influence US government agencies" in connection with a criminal probe in Romania.

The US Department of Justice made the allegation in a Wednesday filing in Los Angeles federal court, where US President Joe Biden's son faces a scheduled Sept 9 trial over tax evasion charges. He has pleaded not guilty.

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ABC said the claim stems from Hunter Biden's work for Gabriel Popoviciu, a wealthy Romanian identified as "GP" in the filing, and who prosecutors say hired Hunter Biden for legal work in late 2015 when Joe Biden was US vice-president.

Reuters could not independently verify that "GP" is Popoviciu.

Lawyers for Hunter Biden did not immediately respond to requests for comment. Prosecutors did not immediately respond to similar requests. The White House declined to comment. Popoviciu could not immediately be located outside business hours.

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In the filing, prosecutors said they plan to present evidence that Hunter Biden and a business associate "received compensation from a foreign principal who was attempting to influence US policy and public opinion and cause the United States to investigate the Romanian investigation of GP in Romania."

Hunter Biden and the business associate "were concerned that lobbying work might cause political ramifications for the defendant's father," and Hunter Biden wanted to conceal the "true nature" of his work for GP, prosecutors added.

GP faced bribery charges in Romania, the filing said.

A federal grand jury charged Hunter Biden last December with failing to pay $1.4 million in taxes between 2016 and 2019, while spending millions of dollars on drugs and various high-ticket items.

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The president's son was also charged with evading the assessment of taxes for the 2018 tax year when he filed false returns. He faces three felony charges and additional misdemeanor counts.

Separately, Hunter Biden was convicted in June by a Wilmington, Delaware, jury of lying about illegal drug use when he bought a handgun in 2018. He has not yet been sentenced.