(Recasts with police reinforcements)

MEXICO CITY, May 17 (Reuters) - Mexico sent federal police reinforcements to a northern border state on Thursday after the bloodiest gunfight in a 5-month-old offensive against drug gangs killed 22 people, including five policemen.

Members of the infamous Gulf Cartel fought a running battle on Wednesday with Sonora state police and troops supported by helicopters, ending at a mountainous ranch where officers killed 15 drug hitmen.

Up to 50 heavily armed drug gunmen riding in sports utility vehicles had abducted police officers and civilians near the giant Cananea copper mine, alerting police who gave chase.

Five police officers died in the shooting and the cartel hitmen also killed two civilians, state authorities said. The gang members fled into the mountains where they were being hunted by hundreds of police.

The state government said there may be more hostages.

Public Security Minister Genaro Garcia said more police had been sent to Sonora, a state of desert and mountains just south of Arizona, to patrol roads and towns.

"After these events, our federal deployment has been reinforced," Garcia told foreign correspondents.

President Felipe Calderon has been unable to contain rampant violence despite sending thousands of troops to fight drug gangs in mostly northern and western Mexican states after taking office in December.

More than 900 people have been killed in drug violence in Mexico this year, most of them in turf battles between the Gulf Cartel from northeastern Mexico and an alliance of traffickers headed by kingpin Joaquin "Shorty" Guzman.

Garcia said Mexico was in talks with the U.S. Border Patrol, the FBI, the DEA and the Bureau of Alcohol, Tobacco and Firearms to put the brakes on guns that enter Mexico destined for cartel members .

The chief of police of the western town of Apatzingan, resigned on Thursday after he was injured in an armed attack while off duty this week.

Five soldiers were killed in an ambush near the town two weeks ago in the heaviest blow to the army yet in the drug fight.

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