Four police officers have been killed and several other people abducted in the northern Mexican state of Sonora.
A group of about 40 armed men entered the town of Cananea near the US border and kidnapped the policemen from their patrol cars, reports said.
Eight of the attackers were reportedly killed by police hours later.
Almost 800 people are thought to have been killed in Mexico in drug-related violence so far this year, despite efforts to crack down on drug gangs.
Earlier this week two senior anti-drugs officers were shot and killed, one in the capital, Mexico City, and one in the northern border town of Tijuana.
There have been frequent attacks on police, military and intelligence officials as the government battles drug trafficking gangs.
According to reports the attackers drove into Cananea in a fleet of cars and surrounded the police, who were in two patrol cars.
Police said a fifth policeman, a petrol station owner and two other civilians were seized and taken into mountainous country outside Cananea.
They were freed hours later after a gunbattle with the attackers in hills near Cananea, the Associated Press reported.
Elsewhere, authorities in the northern state of Coahuila said men disguised as Mexican federal agents captured the state's chief anti-kidnapping investigator, AP said.
Correspondents say the continuing violence in Mexico is part of a struggle between drug traffickers and the government.
President Felipe Calderon sent more than 3,000 soldiers to Tijuana in January to fight trafficking and gang violence.
More than 300 people were killed there in 2006.
A month earlier he dispatched 7,000 troops to Michoacan state on the Pacific coast, where more than 500 people died last year.