CIUDAD JUAREZ, Mexico (AP) - Police officials say four state police officers have been killed and two others injured in two separate attacks.

Chihuahua State Public Safety Department spokesman Samuel Delgado says unknown gunmen opened fire on two plainclothes policemen in an unmarked car early Thursday, killing both.

About four hours later, gunmen opened fire on patrolling officers, killing two and injuring another two. A gas station attendant caught in the crossfire was injured.

More than 1,900 people have been killed in Juarez this year, making it Mexico's deadliest city. Authorities attribute the violence to a turf battle between the Juarez and Sinaloa drug cartels.

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