Police in Mexico City found two severed human heads on a street near a major military base Monday, a grisly tactic of warring drug gangs that has long affected other parts of the country while largely sparing the capital.

Decapitations are frequently carried out by gangs in drug-violence-plagued cities such as the Pacific coast resort of Acapulco and in northern Mexico, often to intimidate or threaten rivals.

But it was the first multiple decapitation in the capital since January 2008, when two heads were found near the city's international airport. Two heads were also found in the same vicinity in December 2007. Those killings were believed to be related to a drug shipment that had been seized at the airport.

The office of Mexico City Attorney General Miguel Mancera said in a statement that one of the heads found Monday had been placed on the hood of a sport utility vehicle, and the other was found on a nearby sidewalk.

The heads were found just before dawn on the side of a busy ring road across from the army's headquarters at Military Camp 1.

Mancera was quoted by local news media as saying Monday that the heads were accompanied by a note referring to the "Mano con Ojos" or "Hand with Eyes" drug gang. The organization has been active in the State of Mexico, which borders Mexico City, and in some southern districts of the capital. Mancera gave no details of what the message said.

The heads were found on a busy ring road across from the army's national headquarters at Military Camp 1.

The Hand with Eyes gang formed after the arrest of Edgar Valdez, aka "La Barbie," a top assassin for the Beltran Leyva cartel until he was detained in 2010.

The alleged leader of the Hand with Eyes, Oscar Osvaldo Garcia Montoya, 36, was arrested in July and told prosecutors he helped carry out or ordered more than 600 killings.