Story highlights Bill de Blasio is interviewed for second time in ongoing state and federal investigations

Mayor has repeatedly denied any wrongdoing

New York (CNN) Federal prosecutors interviewed New York Mayor Bill de Blasio on Friday in relation to an ongoing investigation, his press secretary said in a statement.

The scope of the investigation has not been disclosed, but numerous media outlets citing unnamed sources said that the mayor and his staff are under scrutiny for issues related to fundraising for his 2013 campaign. The office of US Attorney for the Southern District of New York Preet Bharara is leading the probe.

De Blasio has denied any wrongdoing, and his press secretary, Eric Phillips, said Friday that the meeting with federal prosecutors was voluntary.

The meeting lasted four hours and was held at the law office of de Blasio's attorney, Phillips said. The mayor was expected to travel later on Friday to Atlanta to attend the Democratic National Committee's Winter Meeting.

The mayor had not been granted immunity when he sat for questioning, Phillips added. Spokespersons for Bharara's office and the FBI, which typically investigates federal cases alongside prosecutors, declined to comment on the meeting.

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