US prosecutors unveiled new criminal charges against Senator Robert Menendez on Tuesday, alleging he took bribes to help a businessman secure investment from a fund with ties to Qatar's government.

Menendez already faces corruption-related charges in the same case, which he has denied, including conspiring to act as an agent of Egypt and taking bribes and influence peddling for Cairo.

Menendez has rejected calls for his resignation, but in September relinquished his chairmanship of the powerful Senate Foreign Relations Committee.

Menendez allegedly received bribes to assist a businessman, Fred Daibes, who was "seeking millions of dollars in investment from a fund with ties to… Qatar by performing acts" beneficial to Doha, according to the indictment.

It said Menendez had introduced Daibes to a member of the Qatari royal family who was also a principal of the unnamed Qatari investment company.

"Menendez made multiple public statements supporting the government of Qatar" while the company was considering investments into a real estate development owned by Daibes, the indictment said.

Daibes is also charged in the case and has pleaded not guilty, with the trial set for 6 May.

In the Egypt-related charges, Menendez has been accused of accepting hundreds of thousands of dollars in bribes from three New Jersey residents between 2018 and 2022, and of having used his "power and influence to protect, to enrich those businessmen and to benefit the government of Egypt."

Tuesday's superseding indictment said that agents had found over $480,000 in cash stuffed into envelopes "and hidden in clothing, closets, and a safe" during a search of Menendez's home.

Some of the cash was found in jackets emblazoned with Menendez's name.

The 70-year-old veteran Democrat, whose parents immigrated to the United States from Cuba, has previously denied that he had committed any crimes.