US congressman George Santos has been hit with additional criminal charges for inflating his campaign’s fundraising numbers in a bid to qualify for financial and logistical support from a Republican Party committee, prosecutors said.

A 23-count superseding indictment filed on Tuesday in federal court in Central Islip, New York charged the embattled congressman and his former treasurer, Nancy Marks, with falsely telling the Federal Election Commission that their family members had made significant financial contributions.

Marks pleaded guilty last week to a conspiracy charge.

Santos, 35, pleaded not guilty in May to a 13-count indictment charging him with defrauding prospective political supporters by laundering funds to pay for his personal expenses, and illegally receiving unemployment benefits while he was employed.

The 35-year-old political newcomer has pleaded not guilty and resisted calls to resign for lying about his resume.

He is free on $US500,000 ($778,000) bail.