Mexico City  - A team of commandos dressed in police uniforms Friday freed six inmates, allegedly assassins in the service of the Gulf Cartel, from a jail in eastern Mexico, said authorities in the state of Veracruz.

Authorities in the Coatzacoalcos prison, located about 600 kilometres south-east of Mexico City, said some 30 people dressed as officers of the Federal Investigation Agency (AFI) arrived at the jail early Friday morning pretending to be involved in an inmate transfer operation.

Without firing a single shot, commandos made their way to the jail cells and took six alleged members of the group Los Zetas, considered the armed wing of the Gulf Cartel, who had been detained for about a year.

In a different case, Mexican authorities were investigating a human head found Thursday on a vehicle parked by in a residential neighbourhood park of Monterrey, the main industrial metropolis in northern Mexico.

The head belonged to Erick Alejandro Alvarado Munoz, known with the alias "La Gata" (the cat), who had been injured and forced into a vehicle hours earlier, after being chased in his car by several vehicles with armed people through the streets of Monterrey.

In recent years Mexico has been shaken by violent actions between rival drug gangs and against security forces. According to media reports, some 1,100 people have been killed in such violence since January. (dpa)