Federal Police Officers are seen near an abandoned car with two corpses in its trunk in Acapulco, Mexico on December 18, 2014. Guerrero is one of Mexico's poorest and most violent states, where a lucrative drug trade has flourished. Drug trafficking in the state is dominated by the Los Rojos criminal gang, based in the regional capital Acapulco. AFP PHOTO/ Pedro PARDO (Photo credit should read Pedro PARDO/AFP/Getty Images)

MEXICO CITY, March 11 (Reuters) - A 42-year-old woman running for mayor in a violent southwestern Mexican state that sparked the biggest crisis of President Enrique Pena Nieto's administration has been kidnapped and decapitated.

State prosecutors said on Wednesday the body of Aide Nava was found in northern Guerrero, where 43 trainee teachers were abducted and almost certainly massacred last year, sparking an international outcry over criminal violence in Mexico.

A spokesman for the prosecutors said Nava, a candidate from the leftist Party of the Democratic Revolution (PRD), was kidnapped on Tuesday in the town of Ahuacuotzingo, the municipality she hoped to become mayor of in June elections.

The motive for her murder was not clear, although local media said a message had been left with her body from the Los Rojos drug gang, one of the main criminal groups in Guerrero.

Pena Nieto, who pledged to restore order to Mexico when he took office in December 2012, had to contend with a string of major street protests over the disappearance of the students on the night of Sept. 26, 2014, in the city of Iguala.

According to the government, the students were abducted by corrupt local police in league with a drug gang. Iguala's PRD mayor and his wife were accused by the attorney general's office of being the architects of the crime.

More than 100,000 people have died in violence linked to drug cartels in Mexico during the past eight years. (Reporting by Lizbeth Diaz. Editing by Andre Grenon)