The New Jersey Democrat - until recently the chair of the Senate Foreign Relations Committee - is accused of taking actions from 2018 to 2022 on behalf of Egyptian military and intelligence officials.

Menendez entered the plea before US District Judge Sidney Stein in Manhattan.

The 69-year-old said in a statement on Monday that "piling new charge upon new charge does not make the allegations true".

Read more:
Senator: $480,000 in cash found at home was from savings
Bob Menendez charged with bribery

The senator and his wife Nadine Menendez had previously been charged with accepting hundreds of thousands of dollars worth of cash and gold bars from three New Jersey businessmen in exchange for using his influence to benefit Egypt's government and interfere with law enforcement probes into the businessmen.

All defendants pleaded not guilty to those charges last month.

Nadine Menendez and one of the businessmen, Wael Hana, pleaded not guilty to the foreign agent charge on 18 October.

Under the Foreign Agents Registration Act, individuals must register with the department if they act as "an agent of a foreign principle".

Prosecutors said Hana arranged meetings between the senator and Egyptian officials, who pressed him to sign off on military aid.

In return, the businessman put Nadine Menendez on the payroll of a company he controlled, prosecutors said.

The new indictment said both Hana and Nadine Menendez communicated requests and directives from Egyptian officials to the senator.

Bob Menendez has resisted calls from fellow Democrats to resign.