A fifth high-ranking New York City police officer has been reassigned in an unfolding federal investigation into whether officers accepted gifts from businessmen with ties to Mayor Bill de Blasio.

The New York City Police Department said that Andrew Capul, a deputy chief, had been transferred to an administrative post in connection with the ongoing investigation.

Roy Richter, president of the union that represents high-ranking officers, said he was confident that Capul was not a target in the probe and had cooperated with investigators.

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Four other commanders were transferred last Thursday, based on what Police Commissioner William Bratton said was information developed in the investigation.

The probe is examining whether police officers received gifts and travel from businessmen in exchange for unspecified favors, and has centered on two businessmen, Jona Rechnitz and Jeremy Reichberg, according to a source familiar with the matter who was not authorized to speak publicly.

Rechnitz contributed to de Blasio's 2013 campaign, while Reichberg helped raise money for a nonprofit organization controlled by de Blasio advisers to support the mayor's agenda.

The investigation has also included former Chief of Department Phillip Banks, once the police department's highest-ranking uniformed officer, and Norman Seabrook, head of the correction officers union, the source said.

Banks earned $250,000 to $500,000 from unspecified investments from JSR Capital Inc, Rechnitz's real estate firm, according to a financial disclosure report Banks filed in 2014.

Rechnitz's lawyer has declined to comment. Reichberg could not be reached for comment. Banks' lawyer has denied any wrongdoing, while Seabrook has declined to comment.

De Blasio told reporters on Monday he was confident his campaign and administration had not committed any improprieties.

"I hold myself and my administration to the highest standard of integrity," he said.

The 2013 campaign committee has hired Barry Berke, a high-profile defense lawyer, to represent it during the probe, a spokesman for the campaign confirmed on Wednesday.

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The campaign is also returning 2013 contributions made by Rechnitz.

De Blasio said on Monday he had not conferred with legal counsel because he had not had any contact with federal authorities.

"I assume they have my phone number if they want to talk to me," he said.

The investigation led on Friday to the arrest of a former restaurant owner, Hamlet Peralta, for running a $12 million Ponzi scheme. The source said the case was linked to the probe, though court documents do not specify how.