Robert Menendez, the influential head of the US Senate's Foreign Relations Committee, is under investigation by a grand jury in Miami for alleged influence peddling, the Washington Post reported Friday.
"As we have said all along, we welcome any review because Senator Menendez's actions have always been appropriate, and we believe the facts will confirm that," an aide to the politician said in an email.
The US Attorney's office in Miami would not comment on the report.
Menendez has been embroiled for months in an investigation into a well-known Miami doctor and businessman, Salomon Melgen, who contributed large sums of money to the Democrat's campaign.
Melgen is reported to have businesses in the Dominican Republic, and Menendez is alleged to have intervened on his behalf with the US government from his congressional office.
FBI agents recently searched Melgen's office, supposedly in connection with other problems facing the doctor, according to US media reports.
Menendez has publicly acknowledged that he queried government agencies on behalf of Melgen, but said he did so because he was a US businessman with bureaucratic problems in the Dominican Republic.
He has been invited to Melgen's villa in the Dominican Republic on several occasions, and recently had to reimburse the doctor for several trips after admitting to a mix-up with air fares from his re-election campaign last year.
Conservative media assert that Menendez used the services of prostitutes during the visits to the Dominican Republic, but a Dominican woman who had said Menendez paid for her services later retracted the accusation.
"Every day, more evidence emerges that the false smears against Senator Menendez are nothing but an elaborate campaign orchestrated by Republican political operatives," the senator's office said in an email.