MEXICO CITY – Gunmen killed five suspected drug dealers in Ecatepec, a municipality in the Mexico City metropolitan area, police said.

The killings occurred Tuesday afternoon in Laguna Chiconautla, a poor section of the city, inside a shack used to sell drugs.

The gunmen, who were carrying AR-15 assault rifles, also killed three horses and a donkey used by the drug dealers to ply their wares, eyewitnesses said.

Four of the victims died at the shooting scene and the fifth was pronounced death while being taken to a hospital.

A judge in the western state of Jalisco, meanwhile, ordered that 12 soldiers and six police officers arrested for allegedly working for “Los Zetas,” the armed wing of the Gulf drug cartel, be held pending the completion of the investigation.

The security forces members were arrested on March 5 on murder, drug and criminal conspiracy charges, the Attorney General’s Office said.

“These 18 people are linked to the ‘Zetas’ who operate in the city of Aguascalientes,” the AG’s office said.

Army troops in the northern state of Nuevo Leon are on alert after officials were told by a former police officer that drug traffickers planned to retaliate for the recent arrests of six gunmen, the Defense Secretariat said.

The tip was provided by former police officer Jose Carlos Treviño, who is suspected of being the leader of a group of taxi drivers, peddlers and cops who acted as spies for the Gulf cartel in Monterrey, the capital of Nuevo Leon.

Treviño, whose group is known as “Los Halcones,” was arrested earlier this week and told authorities that one of his superiors in the drug cartel gave orders “to take violent action against military personnel” in retaliation for the arrest of the gunmen following a shootout Sunday near Monterrey, the Defense Secretariat said.

The former police officer confessed that he rescued a man known as “Comandante Colosio,” the head of the Gulf cartel in Monterrey, during the shootout, the secretariat said.

Treviño said he picked up the drug trafficker in his patrol car and left him in downtown Monterrey with a “group of people who were traveling in an armored Hummer H2,” the Defense Secretariat said.

Mexico has been plagued in recent years by drug-related violence, with powerful cartels battling each other and the security forces, as rival gangs vie for control of lucrative smuggling and distribution routes.

Armed groups linked to Mexico’s drug cartels murdered around 1,500 people in 2006 and 2,700 people in 2007, with the 2008 death toll soaring to more than 6,000.

So far this year, according to press tallies, more than 2,240 people have died.

Mexico’s most powerful drug trafficking organizations, according to experts, are the Tijuana cartel, which is run by the Arellano Felix family, and the Gulf, Juarez and Sinaloa cartels.

Two other large drug trafficking organizations, the Colima and Milenio cartels, also operate in the country.

Los Zetas, a group of army special forces veterans and deserters who initially worked as hitmen for the Gulf organization, may now be operating as a cartel, some experts say.

The Sinaloa organization is the oldest cartel in Mexico and is led by Joaquin “El Chapo” (Shorty) Guzman, who was arrested in Guatemala in 1993 and pulled off a Hollywood-style jailbreak when he escaped from the Puente Grande maximum-security prison in the western state of Jalisco on Jan. 19, 2001.

Guzman, considered extremely violent, is one of the most-wanted criminals in Mexico and the United States, where the Drug Enforcement Administration has offered a reward of $5 million for him.

Since taking office in December 2006, President Felipe Calderon has deployed more than 45,000 soldiers and 20,000 federal police officers across Mexico in a bid to stem the wave of violence unleashed by drug traffickers.

The anti-drug operation, however, has failed to put a dent in the violence due, according to experts, to drug cartels’ ability to buy off the police and even high-ranking prosecutors. EFE