Ciudad Juarez is caught in a bitter turf war between drug gangs
Gunmen stormed into a drug treatment clinic in northern Mexico, lined patients up against a wall and killed at least 17 of them, officials say.
Several others were injured in the attack in Ciudad Juarez on the Mexico-US border, where more than 1,000 people have died in drug violence this year.
Drug clinics in Juarez have been hit before with traffickers accusing them of protecting dealers from rival gangs.
In other violence, a senior police officer was killed in western Mexico.
Jose Manuel Revuelta, deputy police chief in the state of Michoacan, was killed by heavily armed men in two cars who intercepted the vehicle he was driving. His two bodyguards and a bystander were also killed.
Mr Revuelta, 38, was killed blocks away from police headquarters in the state capital, Morelia. He was appointed to the post just two weeks ago.
Michoacan, the home state of President Felipe Calderon, is the base of one of the country's most violent drug gangs, known as the Family or La Familia.
Wednesday's killings in Ciudad Juarez are the latest evidence of the vicious inter-gang drug war that has seen some 1,400 drug-related deaths in the city so far this year.
According to security officials, hooded gunmen burst into the drug clinic, forced patients into a corridor, lined them up and shot them.
At least 17 died and several were hurt in the attack, which was one of the deadliest in Ciudad Juarez since Mr Calderon launched his crackdown on the drug gangs in late 2006.
Thousands of extra police and troops have been deployed in Ciudad Juarez to try to stem the violence.
Rehabilitation clinics in Juarez have been targeted before. Last year, eight people were killed when gunmen forced their way in.
Cartel members who know they are on a hit list are understood to use such facilities as a safe hiding place, says the BBC's Stephen Gibbs in Mexico City.
Earlier this week, the state security minister, Victor Valencia de los Santos, said that rehab centres had become the breeding ground for criminal gangs.
"In this type of places, the drug cartels are recruiting youngsters from 17 to 23 years of age," he was quoted as saying by Mexico's El Universal newspaper.
The killings came as President Calderon used his annual state of the union address to defend his government's battle against the drug gangs.
"As never before, we have weakened the logistical and financial structure of crime," Mr Calderon said.
His government was dealing a "hard blow" to organised crime, Mr Calderon said, detailing that under his administration, some 80,000 people with presumed links to drug gangs had been detained, including 70 top traffickers.