A Roman Catholic priest kidnapped in Mexico on Monday was found shot dead on Christmas Day. He is the third priest to have been killed in Guerrero state, renowned for drugs crime. Others have been threatened, attacked and injured.

The body of Father Gregorio López Gorostieta was found near Ciudad Altamirano. He had been kidnapped by gunmen from the city's seminary, where he taught, and shot in the head.

Earlier this year, the priest accused Guerreros Unidos, a notorious drugs gang, of abducting and murdering 43 students in September. The remains of just one of the disappeared students has so far been found.

The body of Father John Ssenyondo, a Ugandan priest kidnapped in April, was discovered last month during a search for the students. In September, the badly beaten body of the Father Ascensión Acuña Osorio was in a river near his parish.

Father Gregorio's body was found by police looking for the missing students. Protestors on Wednesday had staged march to the city's cathedral on Wednesday, calling for the return of the missing priests and the students.

They carried banners that said "Enough Already!" and "Return Father Gregorio" and sang hymns.

Bishop Maximino Martinez told AP that a group had been seen lurking around the seminary where the priest taught on the outskirts of Ciudad Altamirano, Guerrero, on Sunday and Monday.

"This is another priest added to those who have died for their love of Christ," Bishop Martinez said. "Enough already of so much pain, of so many murders. Enough already of so much crime. Enough extortions."

Some clergy have earned the enmity of drugs gangs by refusing to perform marriages, blessings or baptisms for their families without the paperwork being completed.

"At times, if they ask for a baptism and you don't do it, they start to threaten you. They want a marriage, or a blessing" for a car or a home, he said, and won't take "no" for an answer," the bishop said.

Nine priests have so far been killed in two years in Mexico, and a further two remain missing.