Sen. Bob Menendez, D-N.J. is "aware" of an investigation being conducted by the Southern District of New York, according to a spokesperson.

Menendez is under a criminal investigation which is being led by federal prosecutors in Manhattan, Fox News has learned.

"Senator Menendez is aware of an investigation that was reported on today, however he does not know the scope of the investigation. As always, should any official inquiries be made, the Senator is available to provide any assistance that is requested of him or his office," Michael Soliman, advisor to Sen. Menendez, told Fox News Digital.

Multiple federal agencies are involved in the investigation, which includes the Federal Bureau of Investigations. The FBI declined to comment.

Sen. Bob Menendez

Senator Bob Menendez, a Democrat from New Jersey, speaks during a Senate Banking, Housing and Urban Affairs Committee hearing in Washington, D.C., US, on Tuesday, May 10, 2022.  (Photographer: Tom Williams/CQ Roll Call/Bloomberg via Getty Images)

A source told Fox News that the investigation is related to a 2015 indictment which involved Mendendez. 

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Mendendez was previously indicted under federal bribery charges, but the case was dropped in Nov. 2017 after a mistral was declared.

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U.S. Senator Bob Menendez (D-NJ) speaks at Seton Hall University in South Orange, New Jersey August 18, 2015. (Reuters)

Prosecutors previously accused Menendez of accepting gifts and donations from a wealthy friend for political influence.