NEW YORK (Reuters) - Four high-ranking New York City Police Department commanders have been transferred in the midst of an ongoing city and federal corruption probe, Police Commissioner William Bratton said on Thursday.

The investigation has focused on whether officers received free trips and gifts from businessmen and examined the activities of the NYPD’s former highest-ranking uniformed officer, Chief of Department Philip Banks, according to a person familiar with the matter who was not authorized to comment publicly.

The department’s Internal Affairs Bureau launched the probe in 2013 and later joined a federal investigation led by the U.S. Department of Justice and the Federal Bureau of Investigation.

“The potential violations under investigation include violations of NYPD rules and policies, the city conflict of interest rules and the federal criminal laws,” Bratton said. “The investigation is examining the conduct of current and former NYPD officers and several others.”

New York media outlets, citing unnamed sources, have reported that investigators have examined connections between police department officials and two Brooklyn businessmen, Jona Rechnitz and Jeremy Reichberg.

Among others, the investigation has looked at Banks, the former chief of department who stepped down in 2014 after he was passed over for commissioner, and Norman Seabrook, the head of the city’s correction officers union, the source said.

Banks’ attorney, Benjamin Brafman, said news stories reporting that the amount of money in Banks’ accounts had raised red flags were “patently false.”

“Not one dollar in any of those accounts can be tied to any corrupt conduct whatsoever,” Brafman said in an emailed statement.

Seabrook declined to comment through a spokesman.

The businessmen, Rechnitz and Reichberg, have ties to Mayor Bill de Blasio and contributed to his election campaign in 2013.

De Blasio told reporters on Wednesday that the two men had not contributed to his 2017 reelection campaign and that he would not accept donations from them while the investigation was ongoing.

A spokeswoman for de Blasio said on Thursday that he is “fully supportive of these investigations to learn the truth.”

A lawyer for Rechnitz declined comment. Reichberg could not be reached for comment, and it was not clear whether he had retained a lawyer.

Bratton said on Thursday that he had transferred three deputy chiefs and a deputy inspector.

“The public has an expectation of a high degree of trust and integrity in its police department,” he said. “We will follow the leads wherever they take us.”

Roy Richter, head of the union that represents high-ranking officers, said media allegations “tarnish the unblemished career records” of the commanders.

“I do not know any of the police commanders to be the subject of the FBI probe and hope the federal investigation is wrapped up quickly to allow them all to defend their reputations in an open forum,” he said.

A spokesman for the U.S. Attorney’s office in Manhattan declined to comment.