Washington DC - Prosecutors unveiled new criminal charges against Senator Robert Menendez on Tuesday, alleging he has sought to obstruct justice as investigators probe him for graft involving Middle Eastern countries.

Menendez already faced corruption-related charges, which he has denied, including conspiring to act as an agent of Egypt, taking bribes and influence peddling for Cairo, and helping a businessman secure investment from a Qatari fund.

The new charges follow the decision of businessman Jose Uribe, who was charged alongside Menendez and his wife, to plead guilty and assist investigators with their probe.

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

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"A superseding indictment was returned by the grand jury... and includes new charges of conspiracy to obstruct justice and obstruction of justice," court documents showed.

The rewritten indictment additionally alleges that Menendez caused his former lawyer to mislead investigators about payments the senator had received from other defendants in the case.

Menendez, who has previously said that he is innocent, did not respond to an AFP request for comment. A trial is scheduled for May.

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.

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."

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