Senator Robert Menendez denied any wrongdoing on Friday and said he was "not going anywhere" after CNN reported the U.S. Justice Department is preparing criminal corruption charges against the New Jersey Democrat.
Citing unidentified sources briefed on the case, CNN said the charges center on allegations Menendez used his office to promote the business interests of a Democratic Party donor and friend in exchange for gifts.
"I have always conducted myself appropriately and in accordance with the law," Menendez said in a statement he read to reporters in Newark, New Jersey.
"I am not going anywhere," the senator said. He did not take any questions.
CNN said Attorney General Eric Holder has given the green light for prosecutors to proceed with charges and an announcement could arrive in coming weeks.
Holder, who was traveling in South Carolina with President Barack Obama, said he could not comment.
Justice Department officials declined to comment.
Federal authorities have probed Menendez's relationship with Florida ophthalmologist Salomon Melgen, a Democratic donor who has been accused of over-billing the Medicare program.
The senator said his friendship with Melgen had spanned decades and they "have given each other birthday, holiday and wedding presents - just as friends do."
Two law enforcement officials told Reuters the Federal Bureau of Investigation had been conducting a major corruption investigation of Menendez for some time, and one said it was nearing completion.
Menendez is the former chairman of the Senate Foreign Relations Committee, where he is now the top Democrat. He has been a critic of the Obama administration's policy on Cuba and Iran, but he is a staunch supporter of the White House on other issues.
Media reports over the past two years alleging wrongdoing by Menendez have not been substantiated. At least one, involving underage prostitutes, has been discredited.
Menendez, who is Cuban-American, is among the most senior Hispanic politicians in the country. He was re-elected to a second Senate term in 2012, and spent 14 years in the House of Representatives.
CNN said the government's case focuses on Melgen and, in part, on plane trips that Menendez took in 2010 to the Dominican Republic as a guest of Melgen.
In 2013, Menendez's campaign repaid Melgen $11,250 for a flight on Melgen's private plane three years earlier.
Prosecutors are focusing on whether Menendez promoted Melgen's business interest in a Dominican Republic government contract for port screening equipment, CNN said.
