Democratic New Jersey Sen. Bob Menendez under federal investigation

Sen. Bob Menendez, D-N.J., is under federal criminal investigation, sources familiar with the matter told ABC News and confirmed by an adviser to the senator.

The investigation is being conducted by federal prosecutors in Manhattan, the sources said. The exact nature of the investigation was not immediately clear.

“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,” said the adviser, Michael Soliman, in a statement provided to ABC News.