MORELIA, Mexico (AP) — State police expected the worst when they ventured into the wild township of Aguililla to serve a single warrant. Commanders sent 42 officers in five trucks.

It wasn't enough. More than 30 suspected drug cartel gunmen were waiting for them Monday, some in vehicles that were apparently armored, prosecutors in Mexico's western state of Michoacan said.

Officials said the gunmen opened up on the police convoy with .50 caliber sniper rifles and AR-15 and AK-47 assault rifles.

Thirteen officers were killed, some of their bodies still inside the patrol trucks when the vehicles were set afire. Nine other officers were wounded.

The attack — the worst on Mexican law enforcement in years — came in a state where violence blamed on drug gangs has jumped in recent months.

Authorities said the state police convoy was ambushed as it sought to enforce a judicial order at a home in El Aguaje, a town in the municipality of Aguililla, which is the reputed birthplace of Nemesio "Mencho" Oseguera, leader of the hyper-violent Jalisco New Generation cartel.

"No attack on the police will go unpunished, and this was a cowardly, devious attack because they laid an ambush in this area of the road," Gov. Silvano Aureoles said.

Images published in Mexican media showed vehicles burning in the middle of a highway and messages apparently signed by Jalisco New Generation, one of Mexico's most powerful and rising cartels. Aureoles said their authenticity was under investigation.

Later in the day, an Associated Press journalist saw two gutted patrol cars at the entrance to El Aguaje surrounded by hundreds of bullet casings. Two police trucks were towed away.

Streets were nearly empty as people apparently decided to stay indoors after the violent events.

After the attack, the area in western Mexico's so-called "hot lands" was reinforced by federal and state security forces, which set up checkpoints to hunt for the assailants.

Michoacan, an important avocado-growing state, has recently has seen a spike in violence that has brought back memories of the bloodiest days of Mexico's war on drug cartels between 2006 and 2012.

In August, police found 19 bodies in the town of Uruapan, including nine hung from a bridge. Later, an area roughly 45 miles (70 kilometers) north of Aguililla was the scene of fierce clashes between members of Jalisco New Generation and regional self-defense groups.

In 2013, civilian groups faced with what they said was state inaction armed themselves in Michoacan to fight the Knights Templar cartel, one of whose bases was Aguililla. They said they took up arms to defend themselves from kidnappings, extortion and killings by cartels. But some of the self-defense or vigilante groups later became infiltrated by cartels and gangs.

The government of former President Enrique Peña Nieto launched a process to disarm and legalize the vigilante groups and incorporate them into official security forces.

Aureoles, the governor, says the self-defense groups haven't returned and has criticized federal authorities for not attacking drug cartels in Michoacan with sufficient force and for negotiating with vigilante groups he refers to as criminals.

Besides avocado orchards, Michoacan for decades has been known for marijuana plantations and the making of methamphetamine. It is home to the port of Lázaro Cárdenas, a key entry point for precursor chemicals used to make synthetic drugs.