NEWARK, New Jersey (AP) — U.S. Sen. Bob Menendez said Friday amid a federal investigation that he has always behaved appropriately in office.

The New Jersey Democrat spoke Friday night in his home state.

A person familiar with a federal investigation into Menendez's relationship with a Florida doctor and political donor says the Department of Justice is expected to bring criminal charges against him in the coming weeks. The person discussed the expected filing of charges on the condition of anonymity on Friday because the investigation is pending.

Menendez has been dogged by questions about his ties to the ophthalmologist, a friend whose medical office was raided by authorities two years ago. Menendez's office earlier issued a statement saying all of his actions have been appropriate and lawful.

Attorney General Eric Holder has declined to say whether he has authorized criminal charges against the senator.

Menendez, who served for more than a decade in the House of Representatives before his appointment to the Senate in 2006, is the top Democrat on the Senate Foreign Relations Committee. He has been critical of the Obama administration's negotiations with Iran on its nuclear program and outspoken in opposition to normalizing relations with Cuba.

He has been dogged for more than two years by questions about his ties to Dr. Salomon Melgen, a Florida ophthalmologist as well as a friend and political donor whose medical office was raided by Florida authorities two years ago.

In particular, Menendez has faced questions about trips he took to the Dominican Republic aboard Melgen's private plane. He has acknowledged taking several actions that could have appeared to benefit Melgen, including contacting the Medicare agency to urge changes to a payment policy that had cost Melgen millions.

His failure to reimburse Melgen for flights between New Jersey and the Dominican Republic on the eye doctor's Canadair Challenger 600s luxury jet was the first serious signal of Menendez' legal troubles in early 2013. Menendez and Melgen had flown at least twice in 2010 between New Jersey to the Dominican Republic, but the trips had gone without reimbursement for more than two years.

The flights were just one vestige of the close relations between Menendez, who took over the powerful Senate Foreign Relations Committee in 2013 when previous chair John Kerry left to become Secretary of State, and Melgen, a multimillionaire who was willing to lavish campaign donations on his friend and allied causes.

The two men often appeared together at Democratic Party and Latino political functions from Washington to Miami. Melgen contributed nearly $200,000 to Democratic Party candidates since 1998, including $14,200 directly to Menendez. And in 2012, during Menendez' re-election campaign, Melgen gave $700,000 to the Majority PAC, a super political action committee for Democratic Senate candidates; the PAC spent more than $580,000 to aid Menendez' campaign.

Menendez has reimbursed Melgen for three plane trips. Last year, the senator disclosed that his campaign accounts had paid a law firm $250,000 for legal costs related to Justice Department and Senate Ethics Committee investigations of his ties to the Floridian.

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Tucker reported from Washington. Associated Press writers Nedra Pickler in Columbia, South Carolina, Erica Werner in Washington and Dave Porter in Newark, New Jersey, contributed to this report.