Nearly 40 people have died
in gun attacks by gangs in two Mexican cities, police say.
Gunmen stormed a rehabilitation centre in the northern city of
Chihuahua, killing 19 and wounding four others.
Another 20 people were killed when armed men launched multiple attacks in the city of Ciudad Madero in Tamaulipas state.
Both cities have been caught up in turf wars between drugs gangs fighting over lucrative smuggling routes.
Chihuahua state police spokesman Fidel Banuelos said the attackers there had left messages accusing the victims of being criminals.
The raid took place on Thursday night, but was only reported on Friday.
A police official told AFP news agency that "more than 30 gunmen arrived aboard six trucks".
They moved to the second floor of the Templo Cristiano Fe y Vida (Christian Faith and Life Temple) and fired large-calibre weapons at patients and employees before fleeing, the official said.
Rehabilitation centres in Mexico have been the target of previous attacks.
Correspondents say such shootings are blamed on drug traffickers, who accuse the clinics of protecting dealers from rival gangs.
Spate of murders In Ciudad Madero, violence began on Thursday and several gunmen were then involved in a series of gun battles and murders that lasted into Friday, officials said.
At the end of it, the bullet-riddled bodies of 18 men and two women were found in five different locations in the city, police said.
Correspondents say Tamaulipas is a battleground for the Gulf drug cartel and its former ally Los Zetas, a criminal group set up by former elite military personnel.
An alleged leader of Los Zetas, Hector Raul Luna Luna, was arrested on Wednesday in the north-eastern city of Monterrey, Mexico's third largest city.
In retaliation, gunmen hijacked cars and temporarily set up at least 10 roadblocks in Monterrey. Armed men also attacked police stations, according to local reports.
President Felipe Calderon, who has deployed thousands of troops to the worst-affected regions along the US-Mexico border, issued a statement condemning the latest shootings.
"They are outrageous acts that reinforce the conviction of the need to fight criminal groups who carry out such barbaric acts with full legal force," he said.