TIJUANA, Mexico -- Federal and state police manned checkpoints within city limits as local police suspended their patrols because soldiers sent to crack down on drug gangs and corruption seized most of their guns on suspicion they aided traffickers.
Tijuana Public Safety Secretary Luis Javier Algorri said that without arms, it was too dangerous for the force of 2,000 police to patrol the streets of the city where 13 officers were shot dead last year.
"This is an unfortunate situation because it leaves agents defenseless and does not allow them to serve the community," Algorri said at a news conference.
By Friday evening, however, many officers had returned to duty without guns but with support from armed state police, said municipal police spokesman Fernando Bojorquez.
President Felipe Calderon sent 3,300 soldiers and federal police to Tijuana on Tuesday to hunt down drug gangs. The soldiers swept police stations and took officers' guns for inspection on Thursday amid allegations by federal investigators that a corrupt network of officers supports smugglers who traffic drugs into the United States.
On Friday, soldiers monitored those leaving and entering Tijuana, while federal and state police manned checkpoints within the city limits.
Dubbed "Operation Tijuana," the mobilization is the second major military offensive against drug gangs by Calderon, who took office on Dec. 1 promising to crack down on organized crime.
Last month, Calderon sent 7,000 troops to his native state of Michoacan in western Mexico, plagued by execution-style killings and beheadings as rival gangs fight over marijuana plantations and smuggling routes.
Drug gangs are blamed for more than 2,000 murders nationwide in 2006 and have left a particularly bloody trail in Michoacan and Tijuana, where more than 300 people were slain last year.
On Friday, state officials said they had found nine bodies in a shallow grave in the city of Uruapan, in Michoacan state.
An anonymous call sent police to an abandoned warehouse Thursday in Uruapan, about 180 miles west of Mexico City. There, officials removed a loose section of flooring and discovered the mass grave, said Magdalena Guzman, a spokeswoman for the state prosecutors' office.
Officials found the bodies of three men and one woman late Thursday. Their feet and hands were tied together, and their mouths were covered with tape. The bodies of five other men were uncovered on Friday. All were in advanced stages of decomposition, indicating the victims were killed some time ago. No suspects were in custody.
Uruapan has been the site of some of Mexico's most brutal slayings, including a Sept. 6 attack in which gunmen dumped five severed heads onto a bar dance floor.
Opposition politicians and residents have expressed doubt that Calderon's highly publicized drug crackdown will have much of an impact.
His predecessor, Vicente Fox, also designated thousand of agents to fight drug trafficking, arresting several alleged top kingpins during his six-year term. But those actions appeared to spark more violence as other traffickers battled to take over the smuggling routes of those killed or detained.