The police chief of this embattled border city resigned after eight months on the job amid a rash of recent drug-related killings.

Omar Pimentel, 38, presented a letter of resignation to Mayor Daniel Pena late Wednesday, hours after police found three charred bodies dumped by the side of a road leading into Nuevo Laredo. Police did not immediately know how the bodies got there or who was behind the killings.

"I thank the mayor for the opportunity to collaborate in the 2005-2007 administration through such an important and key post," Pimentel wrote.

Pimentel, who surrounded himself with at least a dozen bodyguards toting automatic rifles, didn't give a reason for his resignation and didn't answer his telephone Thursday. He had served as director of the city's police academy before being named police chief in July.

On Thursday, Pena announced Nuevo Laredo police administrator Guillermo Landa will serve as interim police chief.

Pimentel's predecessor, Alejandro Dominguez, was gunned down just seven hours after being sworn in last June.

Shortly after Dominguez's killing, the mayor fired half of the police force of 700 officers in an effort to weed out corruption and alleged links to drug traffickers.

Pimentel promised to create a more professional police force, but months later he was still struggling to find qualified replacements.

His resignation comes amid a sharp increase in drug-related violence.

The city of 330,000 across from Laredo, Texas, has been caught in a turf war between rival drug gangs fighting for billion-dollar smuggling routes into the United States.