CIUDAD JUÁREZ, Mexico  Several masked men armed with automatic weapons stormed into a drug rehabilitation center in this violent border city on Wednesday night, lined up recovering drug addicts and alcoholics against a wall and opened fire at point-blank range, killing 17 people and wounding three.

The attack, within sight of the border with the United States, was a shocking new low in the wave of vicious crimes Mexico has endured since President Felipe Calderón began a frontal assault on the nation’s drug gangs in December 2006. Rehab clinics have been a special target in Juárez, with cartels hunting for rivals who might be hiding in the clinics or recruiting in them.

Image Authorities stood outside the drug rehabilitation clinic after the attack by gunmen on Wednesday evening. Credit... Alejandro Bringas/Reuters

After investigators had removed the bodies early Thursday morning and rushed the survivors to the hospital, relatives of the victims at the Aliviane rehab center pushed inside. A thick layer of blood covered the concrete floor, from the entrance to the courtyard to the sleeping quarters. A chained dog had been shot, while another huddled in a corner, unhurt. The smell of death hung in the air.