At least 30 armed men invaded a drug-treatment center in northern Mexico late Thursday night, killed 19 patients and wounded four others, the state-run Notimex news agency reported Friday.

The killings occurred around 11 p.m. at the Faith and Life rehab facility in the city of Chihuahua, located in the border state with the same name.

Witnesses told authorities the armed men marched 23 people outside, lined them up and shot them, Notimex said, citing Director of Police Intelligence Saul Hernandez. The wounded were taken to hospitals under heavy guard, the news agency said.