Gunmen killed 11 people and wounded 10 others at a drug rehabilitation center in Torreon, a city in northern Mexico, police said.

The attack occurred around 9:30 p.m. Sunday at the Centro de Rehabilitacion Tu Vida Sobre La Roca A.C. in the northern section of Torreon, which is in Coahuila state.

The gunmen entered the drug treatment center and opened fire on the people inside, state prosecutors said.

Gunmen working for drug cartels have staged a number of attacks in recent years on drug treatment centers in Mexico, especially in the northern region of the country.

The attacks on rehab centers apparently target individuals who are using the facilities to sell drugs on rivals' turf, officials say.

Gunmen killed 13 people in an attack on Torreon's Centro de Recuperacion de Alcoholicos y Drogadictos La Victoria on June 7, 2011.

Armed men attacked the Anexo de Liberacion y Adicciones treatment center on Dec. 5, 2010, in Ciudad Juarez, a border city in Chihuahua state, killing three people and wounding seven others.

At least 10 gunmen went into the clinic and opened fire, officials said.

Gunmen killed 13 people on Oct. 24, 2010, at a drug rehabilitation center in the northwestern border city of Tijuana.

The attack occurred at the El Camino treatment center in east Tijuana, which is in Baja California state.

Nineteen people were killed and six others wounded in an attack on a drug rehabilitation center in Chihuahua city, the state capital, on June 11, 2010.

Gunmen killed 18 people at a drug treatment center located two blocks from a police station and the Santa Fe international bridge in Ciudad Juarez, which lies just across the Rio Grande from El Paso, Texas, on Sept. 3, 2009. EFE