NEW YORK (WABC) -- Federal agents arrived at Gracie Mansion at around 6 a.m., apparently to subpoena New York City Mayor Eric Adams to appear in federal court at a future date.

About a dozen agents were spotted, some carrying bags, as they entered through the East Gate, accompanied by NYPD officers. They spent at least an hour inside the mayor's residence.

The mayor was served with a summons and they took his cellphone.

Alex Spiro, Mayor Adams' attorney released a statement saying:

"Federal agents appeared this morning at Gracie Mansion in an effort to create a spectacle (again) and take Mayor Adams phone (again). He has not been arrested and looks forward to his day in court. They send a dozen agents to pick up a phone when we would have happily turned it in."

An administration official said earlier Thursday that they had not yet been formally notified of an indictment, and his legal team was unaware of the sealed charge returned against the mayor.

The mayor's attorney issued a video statement from the mayor without confirmation that the mayor had been indicted.

"I have been facing these lies for months ... yet the city has continued to improve," Adams said. "Make no mistake. You elected me to lead this city and lead it I will."

The video appeared to have been recorded at Gracie Mansion, where the mayor met with lawyers and aides late into the night on Wednesday.

He also released a written statement that said, "I always knew that If I stood my ground for New Yorkers that I would be a target - and a target I became. If I am charged, I am innocent and I will fight this with every ounce of my strength and spirit."

The federal indictment charging Mayor Adams and likely others is expected to be unsealed later Thursday.

U.S. Attorney Damien Williams is expected to announce the details of the indictment at a news conference at his office.

The charge against the mayor is not known, nor is how many other people may be implicated in this grand jury's indictment. It is believed to be related to the mayor's fundraising efforts in 2021.

Mayor Adams has no public events on Thursday, per a schedule released early in the morning.

Adams now becomes the first mayor in New York City history to be indicted while in office. If he were to resign, he would be replaced by the city's public advocate, Jumaane Williams, who would then schedule a special election.

New York Gov. Kathy Hochul has the power to remove Adams from office. A spokesperson for Hochul said the governor is aware of the "concerning news reports" and is monitoring the situation, saying "It would be premature to comment further until the matter is confirmed by law enforcement."

Adams, the police officer turned politician, along with members of his inner circle has spent nearly a year under the cloud of federal investigations.

His cell phones were seized and, in recent weeks, the residences of some of his closest confidants were searched by federal agents working on several related corruption probes.

The mayor two weeks ago, accepted the resignation of Edward Caban, his handpicked police commissioner, after the authorities issued a subpoena for his phones.

The mayor's chief counsel, Lisa Zornberg, stepped down. This week, the schools chancellor, David Banks, announced plans to retire at the end of the year. Banks had also turned over his phone to federal authorities.

Banks' younger brothers, Philip, the deputy mayor for public safety, and Terence, also had their phones seized. David Banks' fiancée, Sheena Wright, the first deputy mayor, had her phone seized as well.

ALSO WATCH | Dan Krauth explains the federal investigation

Adams has said that, as a former police officer, he has always followed the rules. He has also said he has known of no "misdoings" within his administration.

He has repeatedly said he wasn't aware of any wrongdoing, dismissing speculation that he would face charges as "rumors and innuendo."

The federal investigations into his administration first emerged publicly on Nov. 2, 2023, when FBI agents conducted an early morning raid on the Brooklyn home of Adams' chief fundraiser, Brianna Suggs.

At the time, Adams insisted he followed the law and said he would be "shocked" if anyone on his campaign had acted illegally. "I cannot tell you how much I start the day with telling my team we've got to follow the law," he told reporters at the time.

Days later, FBI agents seized the mayor's phones and iPad as he was leaving an event in Manhattan. The interaction was disclosed several days later by the mayor's attorney.

Other investigations have focused on city contracts and enforcement of regulations governing bars and clubs.

Only the second African-American to lead the nation's largest city, Adams had been hailed as the vanguard of a new generation of Democratic leader who could both support law enforcement and chart a progressive course coming out of a city-crushing pandemic.

He has led the city through a remarkable drop in violent crime after a COVID-era surge that led business leaders and residents to complaint that New York was collapsing toward the bad old days of the 1980s.

Adams is not expected to appear in court until next week, according to sources.

ABC News and the Associated Press have contributed to this report.

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