When soldiers tried to halt a suspicious-looking SUV that was being escorted through Monterrey by a state policeman, the officer radioed for backup. In minutes, police from 40 patrol cars surrounded the troops, drawing their guns and sending the soldiers diving for cover in an hour-long standoff.

Confrontations like that are happening with increasing frequency in Mexico's wealthiest city as soldiers fight corrupt police officers helping drug cartels _ in addition to taking on the drug dealers themselves.

This year alone, police and soldiers have confronted one another more than 65 times, The Associated Press has learned _ a growing and dangerous trend in the war on drugs.

Things are so bad, the general in charge of army operations in northeastern Mexico told the AP, that he has warned police chiefs his men are ready to open fire on police if it happens again.

"The moment they shoot at us, get in our way, use their guns to protect criminals, they become criminals themselves," said Gen. Guillermo Moreno, who commands troops in Nuevo Leon and Tamaulipas states along the Texas border.

President Felipe Calderon has acknowledged that corruption permeates Mexico's low-paid police at all levels and therefore has opted to combat the billion-dollar drug-smuggling industry by relying primarily on the military, which has seen remarkably fewer cases of bribery by traffickers. His administration also has sent in federal police and soldiers, both of whom are higher paid and usually better educated, to go after police on the take.

As a result, distrust between police and soldiers runs high. But nowhere has it exploded like in Monterrey, an industrial hub two hours from Laredo, Texas.

That point was driven home Wednesday with the brazen killing of army Brig. Gen. Juan Arturo Esparza shortly after he was named police chief in the suburb of Garcia. Five Garcia police were among 10 people arrested in the case Thursday.

Most of the problem comes from the fact that Nuevo Leon has not purged corrupt police from its ranks like other states have.

The police chief of Ciudad Juarez _ a retired army general _ has fired hundreds of officers suspected of corruption in the past year, and the army trains new recruits, many of whom are former soldiers. In western Michoacan state, home to the violent La Familia cartel, state police take regular drug tests and have their guns checked every six months to ensure they have not been used in crimes.

Army generals in charge of each region decide whether to invite state police to work with them, and most have done so. But Moreno said he doesn't trust Nuevo Leon police.

"For the safety of our troops and their families, we carry out our operations by ourselves," he said.

The confrontations have jumped from two in 2008 to 67 this year, Moreno said. They range from soldiers stopping officers who were following them to spy for drug cartels, to exchanges of gunfire with police guarding drug lords. In one incident, a police officer was shot in the leg.

The Oct. 13 standoff involving the soldiers and police from 40 patrol cars ended peacefully, but not before some tense moments captured on video by a TV crew.

The dozens of police who responded to the officer's call for backup lined up to take aim at the troops, who pointed back with high-powered rifles.

Army and police commanders talked face-to-face and ordered their men to stand down. The men obeyed _ but not without some resentment.

"We're all in this together, and we should support each other," a police commander is heard telling one of the soldiers on the video.

"No, we're not," the soldier snaps back. "We have arrested many police officers who are not in this with us."

More than 100 Monterrey police officers have been detained this year on suspicion of links to organized crime. Soldiers have found officers referenced in lists seized from drug traffickers detailing who was receiving bribes.

Many police are suspected of working for the Zetas, a group of former army soldiers-turned-enforcers for the cartel known for its meticulous record-keeping as much as its brutal tactics.

Those arrested include two Nuevo Leon state officers accused of taking part in the abduction of nine soldiers allegedly in retaliation for the army's anti-drug operations.

Officials recently detained two other officers from the same force on suspicion of kidnapping two army lieutenants who were moonlighting as bodyguards for a lawyer. They have not been seen since Sept. 25.

"We believe a significant percentage of these officers have links to organized crime, either by collusion or because they were intimidated and are afraid," Moreno said.

Acting on his recommendations, state authorities in June banned officers from using cell phones during work hours to try to prevent them from tipping off criminals to raids by soldiers and federal agents. They also stripped most state and city police officers of their automatic rifles _ to protect troops. Continued...