A police officer was killed Thursday when gunmen attacked a lockup in the western Mexican state of Michoacan and freed two suspected drug traffickers, officials said.

The suspects were being held at a regional delegation of the Mexican Attorney General's Office in Apatzingan.

Armed men burst into the unit shortly after 7:00 a.m. and subdued the only police officer on duty, Javier Hernandez Ramirez, forcing him to open the cells holding suspects Julio Acevedo Cardenas and Joel Contreras Cardenas.

The intruders then killed Hernandez with a shot to the head.

The escape was discovered about 30 minutes later when the district commander of the Michoacan state police arrived at the unit in Apatzingan.

"It seemed strange to the commander to arrive and find the doors open. On looking for his colleague, he found him shot inside a cell," a source with the AG's office delegation in Morelia, the state capital, told Efe.

Army troops detained the two suspects on Tuesday in Apatzingan in possession of guns and drugs.

Possessing more than 270 kilometers (168 miles) of Pacific coastline, Michoacan also has forests and mountain areas that provide perfect cover for drug production and smuggling.

Illegal drugs are smuggled from Central America into Michoacan and then later moved into the United States.

Apatzingan was the scene in January 2004 of an audacious raid by 50 gunmen who stormed the municipal jail and freed 25 prisoners, including several important figures in the Sinaloa and Gulf drug cartels. EFE