A powerful US senator charged with bribery and extortion after gold bars and hundreds of thousands of dollars in cash were found at his home rejected calls on Monday for him to resign.

"I recognise that this will be the biggest fight yet," Democratic Senator Robert Menendez told reporters at a press conference in his home state of New Jersey.

"I firmly believe that when all the facts are presented, not only will I be exonerated, but I still will be New Jersey's senior senator," Menendez said.

Menendez, 69, is accused of providing sensitive information to the Egyptian government in order to help an Egyptian-American businessman protect his monopoly.

He stepped down "temporarily" as head of the influential Senate Foreign Relations Committee after the charges were unsealed on Friday.

Menendez was defiant on Monday in his first public appearance since the indictment, insisting he had done nothing wrong and there had been a "rush to judgment."

"The allegations levelled against me are just that – allegations," he said. "The court of public opinion is no substitute for our revered justice system."

"Prosecutors get it wrong some time," Menendez said.

"Sadly I know that," he said in a reference to a 2015 corruption case against him which ended in a mistrial.

A number of fellow Democrats, including New Jersey Governor Phil Murphy, have urged Menendez to step down.

Prosecutors said they found more than a half-million US dollars in cash in Menendez's New Jersey home and in his wife's safe deposit box, allegedly received from three New Jersey businessmen seeking his help.

Gold bars worth around US$150,000 and a luxury Mercedes Benz convertible, gifted by one of the businessmen, were also found.

Menendez, his wife, Nadine, and the three businessmen face two counts of bribery and fraud. Menendez and his wife were also charged with extortion.

A senator since 2006 and before that a member of the House of Representatives for 14 years, Menendez has been a Democratic stalwart in Congress for three decades.

He is up for reelection to the Senate next year.

Democrats head into the 2024 elections with a narrow 51-49 majority in the Senate. (AFP)