CIUDAD JUAREZ, Mexico (November 19, 2009)--Police in the Mexican border city of Ciudad Juarez say four state police officers were killed and two others were injured in two separate attacks Thursday.

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 who was caught in the crossfire was injured.

The city across the border from El Paso is Mexico's deadliest city.

More than 1,900 people have been killed there this year.

Authorities attribute the violence to a turf battle between the Juarez and Sinaloa drug cartels.