MESA, Ariz. -- The mayor of Mesa is complaining that unannounced raids by sheriff's deputies looking for illegal immigrants at the Mesa city library and City Hall created the potential for accidental violence or conflict between police agencies.

Mayor Scott Smith said neither the city nor its police department were given any warning of the sweep.

"I believe the safety of our citizens was gravely compromised," Smith said. "I believe we had set the scene where bad things could happen ... and I believe that crosses the line to what law enforcement can and should do."

Dozens of heavily armed Maricopa County sheriff's deputies swept into the Mesa city library and City Hall at about 2 a.m. Thursday looking for undocumented workers. The raid netted three janitors at the library.

Sheriff Joe Arpaio said they are believed to have used fake identification cards to get work at a private contracting company that provides service to Mesa buildings.

Thirteen other workers for Management Cleaning Control LLC were arrested later in the day at their homes, and deputies executed search warrants at city offices after they opened for business on Thursday.

The chairman of the cleaning company, Charles Scudder, said it has been using the national E-Verify system to check the citizenship status of its workers since October 2007. The company "does not hire illegal aliens," Scudder said in a statement.

A Mesa patrolman who stumbled over a sheriff's staging area after midnight questioned deputies on their presence because they appeared to be preparing for a full-scale bust of some type. But Smith said after initially telling the officer nothing, deputies told him they were on a training exercise.

Smith said city officials would have cooperated with any sheriff's probe and handed over documents without a search warrant under state public records laws.

"I believe the activities took place by the sheriff's department yesterday put people at risk," said Mesa Police Chief George Gascon.

Arpaio shot back.

"You know what this is all about," he said. "I'm going to tell you what this all about. It's embarrassment. Don't go around accusing my office and my deptuties about risking the lives of the Mesa citizens."

Arpaio has sent squads of deputies to several Phoenix-area firms in the past six months as he pushes his effort to enforce a new state law barring employers from hiring illegal immigrants. Thursday's raid was the first on a city facility.

No cases have been brought under the state "employer sanctions" law, but several dozen illegal immigrants have been arrested on identity theft and other charges.

Some critics have objected to the raids and to "crime suppression" sweeps the sheriff has done in several cities, including Mesa, saying they are racially motivated. Mesa officials were upset when deputies didn't warn them ahead of time earlier this year of a sweep.

Arpaio has defended his actions and did so again after the latest raid. He said the raid was prompted by a tip to a hot line his office operates from a Mesa employee who told them he was rebuffed by Mesa police when he complained about illegal immigrants.

"It's my jurisdiction too, it's my jurisdiction too, you seem to forget," Arpaio said, noting that he can enforce laws anywhere in Maricopa County.