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 Friday.

Two dozen men armed with automatic weapons entered the “Faith and Life” clinic identifying themselves as police late 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.