MEXICO CITY - Twenty prisoners were killed and 12 others injured Saturday in a skirmish at a Mexican prison bordering the US state of Texas, local media reported.

The violence erupted in the morning after two inmates fought each other in a prison in the Mexican city of Matamoros bordering Texas state, according to an official statement.

Police were deployed to restore order at the scene, it said.

Seven prisoners were killed Thursday in a riot at a prison in the northern city of Monterrey.

Drug-related violence is common in Mexican prisons. Drug cartels often fight turf wars for control of smuggling routes in boarder regions.

More than 45,000 people have been killed in drug-related violence in Mexico since the government dispatched army troops to fight drug cartels in 2006.