The remains of the two police officers were found inside black plastic bags in Union, a town north of the Pacific coast resort cities of Acapulco and Zihuatanejo, the Guerrero state Public Safety Department said in a statement.

The officers had been missing since Sunday. Their bodies were found a day after two municipal officers were killed in Union.

Police later found the bodies of two other, unidentified people wrapped in plastic bags and left near a bridge.

Also in Guerrero, a federal police officer was killed and his partner gravely injured when gunmen ambushed their patrol car, the state's Public Safety Department said.

Authorities did not name suspects in the police killings, but the way in which their bodies were found pointed to drug cartels, which have stepped up attacks on security officers since President Felipe Calderon launched a military-led crackdown on the traffickers.

More than 10,800 people have been killed in gang violence since Calderon took office in December 2006.

Also Thursday, two federal highway patrol officers were killed in a shootout in the northern city of Chihuahua, authorities said.

Three civilians were also killed in the clash, federal prosecutors said in a statement. The statement did not say if the men were involved in the shootout or were innocent bystanders.

Federal authorities announced Thursday they detained 92 local and state police officers in central Hidalgo state who were allegedly protecting the Zetas, a group of hit men tied to the Gulf cartel.

Federal police intelligence coordinator Luis Cardenas told reporters the officers had been working for the gang for at least two years.

Corruption permeates all levels of police in Mexico, a major obstacle to Calderon's U.S.-backed campaign to crush brutal drug gangs. Calderon insists he is cracking down: Last year, his government rooted out more than two dozen high-level government security officials, including a former drug czar, who were allegedly paid to protect the Sinaloa cartel.

Earlier Thursday, police said, gunmen opened fire and hurled an explosive at a disco and restaurant in Boca del Rio, a beach town on Mexico's Gulf coast. Nobody was hurt in the early morning attacks.

Police spokeswoman Laura Leon blamed the attacks on organized crime. Extortionists linked to drug gangs often attack or burn businesses that refuse to pay.