CIUDAD JUAREZ, (Reuters) – Armed gunmen burst into  a drug recovery clinic in the northern Mexican city of  Chihuahua and killed 19 young addicts, the latest in a wave of  attacks on drug rehabilitation centers near the U.S. border,  police said yesterday.

Two dozen men armed with automatic weapons entered the  “Faith and Life” clinic identifying themselves as police late  on Thursday night. They grabbed the 19 patients, aged between  18 and 25, lined them up execution-style and opened fire.  Police found almost 200 bullet casings from different kinds of  guns at the scene.

More than 23,000 people have died in drug-related violence  in Mexico since President Felipe Calderon took office in late  2006 and declared war on drug cartels. Violence in northern  states like Chihuahua has exploded with brazen shootouts and  massacres as cartels battle security forces and fight each  other for valuable smuggling routes to the United States.

Police said Thursday’s attack was the worst single act of  drug war violence to hit Chihuahua, an industrial manufacturing  center and the capital of Chihuahua state, also home to the  country’s worst drug hotspot, Ciudad Juarez.

Calderon, in South Africa to see Mexico play in the opening  game of the soccer World Cup, condemned the killings.

“(These) are outrageous acts that reinforce the need to  fight with the full force of the law criminal groups carrying  out such barbarism,” he said in a statement.

Ciudad Juarez, so overrun by drug violence it is now  considered one of the world’s most violent cities, has seen  similar attacks on drug rehab centers as cartel gunmen hunt  down rival dealers.

Hooded gunmen have stormed at least seven rehab clinics in  the city since early 2008. Two back-to-back strikes last  September killed 28 people.

Cartels, mainly focused on U.S. narcotics consumers, are  increasing battling to provide drugs to home-grown addicts,  creating new turf wars that threaten to further stretch the  country’s security forces.