Mexico's President Felipe Calderon condemned in a Friday statement a deadly Thursday night attack on a drug rehabilitation center that killed 19 people and injured a further four in Chihuahua, the nation's most violent state.

"The events that occurred in the Fe y Vida Rehabilitation Centre are outrages and reinforce the conviction that we must fight criminal groups that carry out such acts with the full force of the law," Calderon said in the statement.

Calderon also expressed his condolences to the families of the dead and wished a swift recovery to the injured.

Mexican broadcasters reported that a gang of 30 armed men invaded the Centre, in state capital Chihuahua City, at around 11 pm on Thursday night. The gunmen selected 23 of the residents and dragged them on to the street, forcing them to kneel and then executing them. The gang then left in six Chevy Suburban brand vans.

Chihuahua newspapers reported that the killers left a note at the scene, which called the residents "pigs, rats, killers, kidnappers and rapists," and said "they died because they deserved to."

This was the second reported attack on the centre this year. According to Chihuhua newspapers, a man and a woman were kidnapped there in April and have not been seen since.

Two similar attacks killed 17 people in El Aliviane and Anexo de Vida, rehabilitation centers in Ciudad Juarez, on the Chihuahua border with US state Texas, which was the world's most violent city during 2009.