Gang members shot down a helicopter in a clash with police in restive western Mexico, killing four people, Reuters reported.

According to the governor of the state of Michoacan Silvano Aureoles, helicopter participated in the operation on detention of leaders of criminal cells in Apatzingan, Mexico. Nevertheless, it is still unknown which of the two local criminal gangs are responsible for the incident.

“During the operation, an official helicopter which was supporting the patrol in area of difficult access was shot down. We lament the death of the pilot, three police officers and a police officer who was injured,” Aureoles said.

It is noted that Michoacan has one of the highest murder rates in Mexico. It is also known as a key state for transportation of drugs from South America to the U.S.