A group of more than 40 armed men abducted and killed four Mexican policemen on Wednesday about 30 kilometers (20 miles) south of the Arizona border, and the anti-kidnapping chief in another northern Mexico state was reportedly kidnapped.

Sonora Gov. Eduardo Bours declined to speculate on a motive for the killings of the four policemen in his state, but Mexico has seen a wave of attacks on police, military and intelligence officials as the government battles drug trafficking gangs.

The assailants drove in 10 to 15 vehicles into the city of Cananea and detained the police who were in two patrol cars, the Sonora state police said in a news release.

The bullet-riddled bodies of the policemen, along with 50 spent cartridges were found on the side of a road hours later. Another policeman, a gas-station owner and an unidentified Cananea resident also were abducted and are still missing, the release said.

State police were sent to reinforce security in Cananea.

Meanwhile, authorities in the northern state of Coahuila reported that men disguised as Mexican federal agents had kidnapped the state's chief anti-kidnapping investigator.

Lucio Tello, a spokesman for the state attorney general's office, said that Enrique Ruiz Arevalo, director-general for investigations of kidnapping and organized crime for the agency, has been missing since Monday, when he was seized as he ate breakfast in a restaurant.

The four kidnappers carried rifles and wore black uniforms with the insignia of the Federal Agency of Investigation, Mexico's equivalent of the FBI, when they grabbed Ruiz Arevalo and another agent in Torreon, 500 kilometers (310 miles) southwest of the U.S. border at Eagle Pass, Texas.

They released the other agent hours later. He said he had been blindfolded, roughed up and insulted.

Tello said the attorney general's office knew of no motive for the abduction.