A state police official who said he wasn´t authorized to give his name told The Associated Press by telephone that the head was found in a plastic bag early Thursday by employees of the office in Villahermosa, the state capital.

Officials are trying to determine the victim´s identity, as well as why he was killed and by whom.

In the past year, beheadings have become common among rival drug cartels, and the heads are often left outside security offices, sometimes with messages warning police to leave local drug lords alone.

Tabasco appears to be increasingly targeted by traffickers, who police suspect opened fire on the car of Tabasco state police director Francisco Fernández, injuring him and killing his driver last week.

Fernández, a retired general, had worked as a military attache in Mexico´s embassies in Panama and Washington, and also led the anti-drug units in the northern states of Chihuahua, Durango and Sinaloa.

TWO COPS MURDERED

Two municipal police officers were killed and two others wounded in an attack that took place just outside the northern industrial city of Monterrey, authorities said Thursday.

The Nuevo León attorney general´s office said the police officers were attacked Wednesday night by gunmen armed with assault rifles.

One officer died on the spot and another succumbed in a nearby medical clinic.

The incident reportedly occurred around 11 p.m. as the four officers were sitting in two parked patrol cars.

Several attackers fled the scene of the shootings in a gray Chrysler Stratus with tinted windows, according to eyewitnesses.

A few hours after the shootings, police began pursuing a GMC Yukon SUV that, after a chase, crashed into a truck on the highway to Laredo. Authorities arrested three people.

They were carrying AK-47 assault rifles equipped with laser sights and were sporting bulletproof vests.

It is not yet known whether the trio who were arrested participated in the deadly attack on the policemen.

The incident occurred a few hours after a group of gunmen armed with assault rifles killed four people and wounded four others inside a jewelry store in downtown Monterrey.

One of the dead in that incident turned out to have been a high-ranking police officer involved in drug enforcement, Monterrey Public Safety Secretary Amado Medina said.

Medina said initial reports suggested robbery was the motive, but police later confirmed that three of the victims were being pursued by a group of gunmen armed with AR-15 and AK-47 assault rifles.

Medina said the three individuals took refuge in the jewelry store and the gunmen opened fire on them and a security guard.

"The four people died inside the store and four (others) were reported wounded," Medina said.

MASS RESIGNATIONS

The wave of shootings targeting police officials in the state of Sonora prompted the resignation of 19 local policemen in the state capital of Hermosillo.

Seven police officials have been murdered in Sonora - five of them in Hermosillo - since Feb. 26.

Hermosillo police chief Raúl Chávez on Thursday confirmed that the 19 policemen had submitted their resignations.

Chávez told reporters that the overwhelming majority of these policemen resigned at the request of their families, who feared for their safety.