Investigators in the northern Mexico state of Durango said they found the remains of 10 men and one woman in mass graves in the state capital Wednesday, bringing the total of bodies recovered there to 121.

The Durango state prosecutors' office said in a statement that the remains were uncovered by military personnel who have been excavating at about four sites in the city, which is also known as Durango.

The search has been under way for about a month at pits where drug gangs are believed to have buried victims.

The Durango graves are the second such discovery in a month. A total of 183 bodies have been unearthed in 40 pits in the northeastern border state of Tamaulipas.

Mass graves have become an increasingly common discovery in Mexico, with drug cartels using the sites to dispose of enemies and other victims amid increased fighting among rival gangs. More than 34,600 people have died in drug-related violence since President Felipe Calderon deployed thousands of federal security forces four years ago to fight traffickers.

Authorities in Durango state say the discovery of mass graves there has not brought out many relatives of missing people, perhaps because families are too frightened to come forward.

As Mexicans braced for demonstrations scheduled for the weekend to protest ongoing violence associated with the anti-drug offensive, Calderon issued an impassioned appeal in a televised speech Wednesday for Mexicans to stick with fight, though he acknowledged it will take time.

"Backing off from the fight is not an option," Calderon said. "If we retreat, we are going to allow gangs of criminals to roam the streets of Mexico, attacking people with no one to stop them."

Calderon criticized "those who, with good intentions or bad, are trying to stop the government from acting." He said "nobody likes violence," but warned that peace "is not a goal that will be achieved with false solutions."

He said Mexico needed to reform its police forces and judicial system to be able to fight the drug cartels.

"These are changes that will take time in order to be carried out, but it is worth the effort, because it is the only solid and lasting basis for the future."

Also Wednesday in the Pacific coast state of Guerrero, state police said a man's dismembered body was found in four plastic bags at a shopping mall in the state capital, Chilpancingo.

Police found a handwritten message of the kind frequently left by drug cartels; in keeping with policy, the contents of the message were not revealed.