CIUDAD JUAREZ, Mexico, Sept 16 (Reuters) - Suspected drug hitmen have killed 10 patients in a Mexican rehabilitation clinic, the second such attack this month in the city of Ciudad Juarez on the U.S. border, authorities said on Wednesday. Drug gangs have targeted rehab clinics in the manufacturing city across from El Paso, Texas, accusing them of protecting dealers from rival gangs. State attorney spokesman Vladimir Tuexi said the victims, nine men and one woman, were killed late on Tuesday as they finished praying before going to bed.