Eric L. Adams, a retired police captain who was elected as New York City’s 110th mayor nearly three years ago on a promise to rein in crime, has been indicted following a federal corruption investigation, people with knowledge of the matter said on Wednesday.

The indictment remained sealed on Wednesday night, and it was unclear what charge or charges Mr. Adams will face. But the federal investigation has focused at least in part on whether Mr. Adams and his campaign conspired with the Turkish government to receive illegal foreign donations.

When the indictment is made public, Mr. Adams will become the first New York City mayor to face a federal charge while in office.

The indictment promised to reverberate across the nation’s largest city and beyond, plunging Mr. Adams’s embattled administration further into chaos just months before he is set to face challengers in a hotly contested mayoral primary.

In a statement, Mayor Eric Adams said he had done nothing wrong.

“I always knew that if I stood my ground for New Yorkers that I would be a target — and a target I became,” he said. “If I am charged, I am innocent and I will fight this with every ounce of my strength and spirit.”

Brendan R. McGuire and Boyd M. Johnson III, partners at WilmerHale who represent the mayor, did not immediately respond to requests for comment.

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