Updated

Four police officers and seven civilians accused of working for Mexico's powerful Gulf drug cartel were flown to the capital Sunday for prosecution.

The four municipal officers, detained in Nuevo Laredo, across the border from Laredo, Texas on Saturday, had allegedly funneled police and military information to the cartel by radio, Public Safety Department spokesman Edgar Millan said.

Authorities previously said they were arrested for carrying unregistered guns.

"The power of criminal organizations has permeated the police," Millan said, adding that internal investigations are underway to weed out corrupt officers.

Police corruption is widespread in Mexico, particularly in states like Tamaulipas plagued by organized crime. In October, 25 federal police officers were detained in the state on suspicion of providing protection for the Gulf drug cartel.

Along with the four officers, seven people suspected of working for the Gulf cartel were detained in various parts of Tamaulipas state and transported to the capital Sunday. Among them was a U.S. man identified only as Marcos Estrada Delgado.

Authorities did not give Estrada's age or home town, and the U.S. Embassy said it hadn't been contacted about his arrest.

The arrests came after two weeks of bloody clashes along the border between federal agents and gunmen who allegedly work for the Arellano Felix and Gulf cartels.

A federal agent and a gunman were killed Thursday in a three-hour fire fight in Tijuana, days after three police officials and one of their wives were shot dead.

An officer filling in for one of the slain officials was kidnapped Saturday night by a group of armed men while he drove his car, Tijuana municipal police said. His family was later brought to a police station for protection.

Earlier this month, four other federal agents were killed and 13 injured in shootings in Michoacan state and Tamaulipas.