The Washington Post is reporting that the FBI is investigating allegations that U.S. Sen. Bob Menendez solicited prostitutes while traveling in the Dominican Republic but has so far failed to substantiate the claim.

According to the Post, the investigation includes the allegations that some of the prostitutes were underage.

The agency also is looking into Menendez's role in advocating on behalf of friend and donor Salomon Melgen over a port security contract that a Melgen-owned company holds with the Dominican government, the Post is reporting.

As he has since the allegations first surfaced in November, Menendez vehemently denied any interaction with prostitutes.

“As we have said all along, Senator Menendez welcomes any review because his actions have been appropriate, and we believe the facts will confirm that,” a Menendez aide told the Post.

The revelation that agents are looking into the allegation from an anonymous tipster and two women claiming to be Dominican prostitutes that was first carried by the Daily Caller is the latest negative headline for Menendez, who has withstood a torrent of bad press over the allegations and further reports from the Post and the New York Times that he advocated more than once with the U.S government on Melgen's behalf.

The senator from Hudson County also faces a Senate ethics investigation over at least two flights he took aboard a Melgen-owned plane.  Menendez reimbursed Melgen's company for the flights, but not until two years after he took them.

Menendez should be riding high after ascending earlier this month to the chairmanship of the powerful Senate Foreign Relations Committee, however that news has been largely drowned out by the more damaging allegations.