Mexican authorities say attackers have killed four members of a civilian police patrol in the turbulent southern state of Guerrero. Two official policemen and two gunmen have also died in the border town of Rio Bravo.

The Guerrero state attorney general says seven members of the community police came under attack while patrolling the streets of Tixtla, which is home to the teachers college where 43 vanished after being detained by official police.

The "comunitarios" are civilians allowed to carry weapons and defend their towns in many parts of rural Mexico where official police forces are mistrusted. They have often clashed with organized crime gangs.

Officials in Tamaulipas state on the Texas border say the deaths there came in separate clashes between police and gunmen.