Mexican army soldiers detained a suspected Los Zetas drug cartel hit man accused of taking part in mass killings of bus passengers in the northern town of San Fernando, officials said.

Abraham Barrios Caporal and two other reputed members of a Zetas cell were arrested in the Gulf coast port city of Coatzacoalcos while they were guarding a kidnap victim, the Defense Secretariat said in a statement.

In the operation, "two rifles, two handguns and a vehicle with false license plates" were confiscated from the suspects, the statement added.

The secretariat said Barrios confessed to participating in the killing and clandestine burial in mass graves of people in San Fernando, a town in the northeastern border state of Tamaulipas, saying he acted on the orders of Salvador Alonso Martinez.

The suspect said the reason for grabbing people off of buses in Tamaulipas was to "identify possible members" of the Gulf cartel, which has been locked in a brutal turf war with Los Zetas, its former armed wing.

Over the past three months, Mexican authorities have discovered 193 bodies in 47 clandestine graves in San Fernando, mostly people who had been traveling in buses to the U.S.-Mexico border.

Barrios confessed that during the massacres he served as second-in-command to Martin Omar Estrada, the Zetas' boss in the Tamaulipas town of Mendez, but that all the members of the cell fled San Fernando in April to avoid arrest.

Drug-gang violence intensified in Tamaulipas after Los Zetas split from the Gulf cartel to go into business for themselves and began fighting for control of several lucrative territories.

Founded by deserters from an elite Mexican special forces unit, Los Zetas is regarded as the most brutal of the country's drug cartels.

Members of Los Zetas also are accused of carrying out the August 2010 massacre of 72 undocumented immigrants at a ranch near San Fernando.

The group has drawn the ire of older, established cartels through its extensive involvement in extortion, kidnapping for ransom and robbery, crimes that the other drug mobs generally eschew out of a desire to avoid antagonizing the general public.

Over the past four-and-a-half years, turf battles among drug cartels and clashes between the criminal gangs and security forces - including thousands of army soldiers deployed by President Felipe Calderon's administration to drug war hotspots - have left some 40,000 dead.