The Senate Ethics Committee is reviewing allegations that Sen. Robert Menendez (D-N.J.) accepted inappropriate gifts from a Florida doctor. (Chip Somodevilla/GETTY IMAGES)

The Senate Ethics Committee is reviewing allegations that Sen. Robert Menendez accepted inappropriate gifts from a Florida doctor who has flown the New Jersey Democrat to his estate in the Dominican Republic, a senior member of the panel confirmed Thursday.

Sen. Johnny Isakson (Ga.), the ranking Republican on the committee, said the panel saw reports of the FBI raid Tuesday on the West Palm Beach offices of Salomon Melgen, a Menendez friend and political supporter who is also in an $11 million tax dispute with the Internal Revenue Service. That was followed by Menendez’s confirmation Wednesday night that he wrote a personal check of more than $58,000 to pay for flights on Melgen’s private jet to his Dominican estate — for a pair of trips there more than two years ago.

“The Senate Ethics Committee is aware of the article in the Miami Herald and other media outlets, and we are following established procedures,” Isakson said Thursday, declining to discuss any details of the review.

Menendez has denied any wrongdoing. His staff has said that most of his trips to visit Melgen in the Dominican Republic were paid for out of his own pocket and that the two trips he did not pay for were an oversight. A statement issued Wednesday also vehemently denied reports, mostly in the conservative news media, that he slept with prostitutes on the island, where prostitution is legal.

“Senator Menendez has traveled on Dr. Melgen’s plane on three occasions, all of which have been paid for and reported appropriately. Any allegations of engaging with prostitutes are manufactured by a politically-motivated right-wing blog and are false,” his office said in a statement.

Officials at the Justice Department declined to comment Thursday about the nature of its raid on Melgen’s office, which went on for several hours overnight.

Senate Majority Leader Harry M. Reid (D-Nev.) has stood behind the embattled senator. “First of all, Bob Menendez is my friend. He’s an outstanding senator,” Reid said Thursday, directing any detailed questions to Menendez’s office.

The investigations come at a particularly troubling time for Menendez and Democrats, just as Menendez steps into a new role as chairman of the Foreign Relations Committee. That makes him the top diplomat on Capitol Hill, someone tasked with greeting heads of state visiting Washington, and affords him the kind of public profile that prompts regular appearances on the Sunday morning political talk shows. Last week, Menendez presided over outgoing Secretary of State Hillary Rodham Clinton’s testimony about the U.S. response to the Sept. 11 attack on a mission in Libya and the confirmation hearing for Sen. John F. Kerry (D-Mass.) as her successor.

The only Latino among Senate Democrats, Menendez was chosen to participate in a bipartisan group of senators who unveiled a strategic framework for comprehensive immigration reform amid much fanfare Monday.

Reid’s gesture signaled that Democratic leaders were not abandoning Menendez as he begins what could be a long legal and ethics process. Two days earlier, Reid rejected out of hand any suggestion of wrongdoing by Menendez, telling reporters to “consider the source” because the reports first emerged on the Daily Caller, a conservative Web site that published the stories just before Election Day. The issue was originally regarded as a partisan dispute just before Menendez’s election. But the seriousness of the allegations heated up with the FBI raid and the revelations that repayments to Melgen were made so long after the trips occurred.

Senate rules and federal law forbid expensive gifts unless the lawmaker has a longtime friendship with the person giving the gift. Otherwise, the rules require a prompt repayment for the thing of value, according to ethics experts. If a lawmaker accepts the gift from a friend, it would have to be revealed as such in annual financial disclosure forms that are made public every June.

Menendez did not pay Melgen until two months after New Jersey Republicans first asked the ethics panel to investigate, and the trips were not reported on his disclosure forms.

Menendez, 59, who is divorced, is one of the most prominent Cuban Americans, with deep support in his home town of Union City, sometimes called “Little Havana North,” and in South Florida. He has two grown children active in politics. Elected to the House in 1992, he served in the Democratic leadership there until he was appointed to the Senate in late 2005 and has since won two full terms.