A police officer in a red cross ambulance treats one of the dozens of teachers injured during their protest in Acapulco, Guerrero State, Mexico on February 24, 2015. (Agence France-Presse)
Mexican federal police rejected accusations by a teacher's union on Wednesday that a 65-year-old protestor died after being beaten by officers during a demonstration in Acapulco.
Some 5,000 protestors demanding better pay and justice in the case of 43 missing trainee teachers had been blocking access to the Pacific resort city's airport for six hours on Tuesday when 800 federal police intervened.
Federal authorities say the officers broke up the protest after a bus used by the protestors drove into the police line, injuring seven officers, and then hit reverse toward demonstrators.
The teachers' CETEG union denied involvement in the bus attack.
At least 15 protestors were injured in the melee, officials said.
Manuel Rosas, a CETEG spokesman, said retired teacher Claudio Castillo, who had health problems, was beaten by police officers before he died.
While Castillo was getting medical attention, "a group of federal police removed the paramedics and continued to hit him," Rosas said, citing witnesses.
A Guerrero state civil protection official said separately that Castillo died of head trauma in an ambulance.
But Monte Alejandro Rubido, the national security commissioner, said that an autopsy showed that Castillo had injuries to his thorax and abdomen, and punctured lungs.
The medical report concluded that Castillo died due to "deep trauma to the thorax. It is believed that the injuries were due to crushing," he said, adding that there was no head injury.
"The information indicates that the death was not the result of the clash between protestors and federal police. The death is very possibly due to another event," Rubido said.
He said the cause of death is under investigation.
Authorities detained 106 people and released all but eight of them. Charges are pending.
Federal police Chief Enrique Galindo said officers prevented the protestors from heading to an international tennis open hosted by Acapulco.
Angry at the retired teacher's death, protestors marched on Wednesday in Chilpancingo, capital of Guerrero, where Acapulco is located.
Mexican authorities have battled accusations of brutality in the past year.
Guerrero has been the scene of frequent protests over the disappearance of the 43 college students, who are presumed dead.
Authorities believe the young men were abducted by corrupt police in the city of Iguala in September and delivered to a drug gang, which slaughtered the group.
Germany's federal commissioner for human rights policy, Christoph Straesser, was visiting the missing students' college in Ayotzinapa, near Chilpancingo.