Alejandro Arcos was sworn in last Monday as mayor of Chilpancingo, a southwestern city which is the capital of Guerrero state, where Acapulco is located.

The area has long been plagued by drug violence and criminal gangs.

Unverified reports said Mr Arcos had been beheaded. Police have not confirmed any details of his death, but were pictured at a scene in Chilpancingo where the body was reported to have been found.

"His loss mourns the entire Guerrero society and fills us with indignation," Guerrero governor Evelyn Salgado said in a statement.

The state attorney general's office has said it is investigating Sunday's murder.

The latest violence came just three days after the new city government's secretary, Francisco Tapia, was shot to death.

Alejandro Moreno, a Mexican senator and the national leader of the Institutional Revolutionary Party, said: "They had been in office less than a week.

"They were young and honest public servants who were seeking progress for their community."

He also called on the federal attorney general's office to lead the investigation into the murders given "the situation of ungovernability in Guerrero".

The state has become one of the most dangerous in Mexico for aspiring and elected public officials.

At least six candidates for public office were killed in Guerrero ahead of elections at the beginning of June.

Last year, officials said a demonstration held by hundreds of people in Chilpancingo had been organised by criminals to secure the release of two gang leaders arrested for the possession of drugs and weapons.

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The demonstrators blocked most traffic on the road between Mexico City and Acapulco for two days.

They fought security officials before using a police truck to ram down the gates of the state legislative building.

A number of police, state and federal officials were then taken hostage - before being released when the demands set by the demonstrators had been met.