PITTSBURGH — Mayor Bob O'Connor, who remains hospitalized for treatment of a rare form of cancer, fired three top staff on Thursday, but declined to say why.

"The mayor's been saddened and disappointed by the actions of some of his staff during his convalescence. ... He had no alternative but to terminate them," spokesman Dick Skrinjar said Thursday. He refused to elaborate.

Dennis J. Regan, who had been director of intergovernmental affairs, replaced B.J. Leber as chief of staff. George Specter was named acting city solicitor, replacing Susan Malie. Budget Director Scott Kunka will assume the duties of the finance department, replacing Paul Leger.

In a statement, the three said it was a "privilege to serve Mayor O'Connor and the people of Pittsburgh. Our thoughts and best wishes are with him for a speedy recovery." They said they would have no further comment.

The firings came two days after the release of a memo by Malie in which she questioned whether city council should approve a new head of general services, Yarone Zober.

In past administrations, the solicitor was often named acting mayor when the mayor was abroad or temporarily unable to perform his duties.

O'Connor's attempts to have Zober approved indicates he does not trust other department heads, said Joseph Sabino Mistick, a former top aide for mayor Sophie Masloff and a political analyst and an associate professor at Duquesne University School of Law.

HARRISBURG — The Pennsylvania National Guard can allow as many as 500 soldiers and airmen to volunteer to patrol the Mexican border for as long as three months under authorization Thursday from Gov. Ed Rendell.Deployments in increments of 100 guardsmen will take place through September, the Guard said. The federal government will pay the cost for them to participate in Operation Jump Start, which is designed to stop the flow of illegal immigrants over the southern border.Members of the Pennsylvania Guard who volunteer for the duty will help operate surveillance systems, analyze intelligence, install fences and vehicle barriers, build patrol roads, and provide training.