Gunmen have killed 10 people at a drug treatment center in the northern Mexican border city of Ciudad Juarez, the second such mass killing this month.

A spokesman for the Chihuahua state police said neither the gunmen's identities nor a motive for the attack have been established.

Eighteen people were killed at a different drug center in the city on Sept. 2.

Officials said then that drug gangs may be using the centers to recruit dealers or to eliminate rivals who use them as hideouts.

Nine women and one man were killed in the new attack, just before midnight Tuesday at the Anexo de Vida center. Two people were seriously wounded.