Two people were killed Thursday when locals protesting alleged water contamination by a pork processing plant clashed with police in the Mexican gulf coast state of Veracruz. Residents of the community of San Antonio Limon had been blocking a road demanding government action against the operation, which they said was responsible for polluting the aquifer and using too much water.

State security forces arrived Thursday in the community, also known as Totalco, and protesters said police began beating them and opened fire.

Brothers Alberto and Jorge Cortina Vázquez, aged 22 and 27 respectively, were killed, according to the Veracruz state prosecutor’s office, which opened an investigation.

A third brother, Carlos Cortina Vázquez, said his brothers were not even at the roadblock.

“They were just passing by and when they (the police) started to fire everyone ran,” he said. “That’s when they started shooting at them like they were animals.

Residents said they tried to hide in their homes but some 400 police who arrived chased them. Some showed shell casings they said came from security forces’ guns.

In a statement, the Veracruz state prosecutor’s office said it had undertaken “an exhaustive investigation to clarify the unfortunate events in Totalco.”

The Veracruz state interior agency, which is responsible for security, said in a statement that the protesters had been holding two state police officers and had threatened to kill them. They said the protesters had not been open to dialogue.

“Closing the dialogue by the same group of people worsened the situation,” the agency said. The statement added that it was the second time demonstrators had closed the highway for more than two days. It said the case would also be investigated by state police internal affairs.

Three members of the state security forces were injured, the statement said.