MEXICO CITY – Six federal agents have been arrested on suspicion of passing information to a group of powerful drug lords, a spokesman for the Attorney General's Office said Wednesday.

The agents worked for the anti-drug-trafficking intelligence unit of the Attorney General's office, the spokesman told reporters on condition of anonymity because his office prohibits him from being named. None were prosecutors, but all had various coordination responsibilities during arrests, interrogations and the transfer of prisoners.

The infiltration of drug gangs into the ranks of police and federal agencies has long been endemic in Mexico. It stands as a major obstacle in President Felipe Calderón's fight to destroy the cartels, using thousands of soldiers and federal police deployed across the country.

The six agents are suspected of leaking information to the Beltran Leyva brothers, who head one of the most feared drug-trafficking organizations in Mexico.

The brothers have long been tied to the Sinaloa drug gang, which operates along Mexico's northwestern Pacific coast. But authorities suspect they have been feuding with Sinaloa leader Joaquin Guzman since the January arrest of one of the brothers, Alfredo Beltran Levya.

The Attorney General's Office had announced the arrests of the six agents in an earlier statement, but did not say who had been receiving the leaked information. The statement said the agents were arrested last week, and a judge has ordered them jailed while the investigation continues. They have not been charged.

The spokesman said the Attorney General's Office began suspecting informants within its ranks when sensitive information about ongoing investigations started appearing in the local news media. He said the six agents are suspected of passing data to the Beltran Leyva brothers both directly and through the media. Their leaks helped thwart several federal operations, the spokesman said, without giving details.

The arrests come amid outrage over the alleged involvement of Mexico City detectives in the kidnapping and killing of a 14-year-old boy.

Abductions, along with other violent crime, have been on the rise in Mexico. An average of 65 kidnappings per month were reported from January to May of this year, compared to 62 per month for all of 2007, according to figures from the Attorney General's Office.

So far this year, 323 abductions have been reported, compared to 751 for all of last year. However, many kidnappings in Mexico are believed to go unreported. Distrustful of police, many people prefer to negotiate with the captors on their own.