"The bottom line is we raised concerns with [Centers for Medicare and Medicaid Services] over policy and over ambiguities that are difficult for medical providers to understand and to seek a clarification of that," Menendez said, according to a report in Univision.

He also rejected the notion that he had attempted to influence the agency on behalf of his friend and donor, saying his actions were "much different" than questions about his contact with federal officials had suggested.

Melgen's home and clinic were raided by the FBI earlier this month, although it is not clear why the federal government is investigating him. State records show that Melgen also stands accused of owing millions in back taxes.

But Melgen has become an increasing liability for Menendez, who was recently named the chairman of the Senate Foreign Relations committee and had been a key proponent of the upper chamber's immigration reform package.

The Miami Herald reported that Menendez referenced a contract the government of the Dominican Republic had awarded to a company owned by Melgen during a July hearing of the Foreign Relations Committee.

The conservative website The Daily Caller has also reported that Menendez solicited prostitutes why staying at Melgen's home and using his yacht in the Dominican Republic. A nonpartisan watchdog group also posted an email exchange with a man claiming to have interviewed three prostitutes that testified to having been hired by the lawmaker.

But Univision contacted one of those women, who claimed to have never been a prostitute and said she did not recognize Menendez. And the lawmaker himself has adamantly denied the allegations.

“The smears that right wing blogs have been pushing since the election, that is totally unsubstantiated — it's amazing to me that anonymous, nameless, faceless individuals on a website can drive that kind of story into the mainstream,” Menendez told CNN on Monday. “The bottom line is all of those smears are absolutely false.”