ROME (AP) — Rome's mayor vowed Friday to keep governing despite a top City Hall official's arrest in a corruption probe, the latest blow to hit the populist 5-Star Movement's highest-profile official.

Mayor Virginia Raggi emphasized that Raffaele Marra, the head of City Hall personnel, was left over from previous administrations.

"We trusted in him, probably we made a mistake," she said, apologizing to the people of Rome, the political movement and its founder Beppe Grillo.

She pledged full cooperation into the probe, which involves the purchase of homes from 2013, when Marra worked for another administration. A contractor also has been arrested.

"The administration continues. Dr. Marra is not a member of this administration but one of 23,000 employees" of the city of Rome, Raggi said. Alluding to references to Marra as her right-hand man, she said that title goes to "the citizens of Rome, and it is for them I work without a rest."

The arrest came a day after police searched City Hall and seized records about disputed city appointments, and follows the resignation of Raggi's top environmental adviser, who is the subject of a separate investigation.

The setbacks renewed pressure on Raggi's administration. Her party, 5-Star Movement, has been pressing for a new parliamentary election following the political crisis that forced Italy to form a new government in recent days.

In Milan, Mayor Giuseppe Sala has announced he will step aside after he reportedly was added as a suspect to an ongoing investigation into contracts for the Expo 2015 World's Fair, which he ran before his election. Sala said late Thursday that he was notified only by the media that he had been placed under investigation and that he was unaware of the allegations against him.

Sala's name was added to the suspect list after a judge refused a prosecutor's request to archive the case. The chief Milan prosecutor, who has taken over the case, has requested another six months to complete the investigation.