By Alistair Bell

MEXICO CITY, Feb 16 (Reuters) - Mexico's increasingly brazen drug cartels may have been behind a bomb blast in the center of the capital in what would be a major escalation of a war with President Felipe Calderon's government.

While a small leftist rebel group has bombed energy installations in the last year, police say early evidence from Friday's explosion points more toward a bungled attack by drug gangs that killed over 2,500 people last year in a turf war.

The homemade bomb, attached to a cell phone for activation, went off prematurely near Mexico City's security ministry, killing a man who was believed to have been handling it.

Initial suspicions fell on drug gangs like the Sinaloa Cartel headed by Mexico's most-wanted man, Joaquin "Shorty" Guzman, which has suffered most in recent weeks from an army-backed drive against drug violence by Calderon.

Security forces arrested one of the Sinaloa Cartel's main money launders last month and the gang has lost weapons and cash in police seizures in Mexico City in recent days.

Mexico's chief prosecutor, Rodolfo Felix Cardenas, suggested the cartels that smuggle cocaine and methamphetamine to the United States, may have planned the bomb attack.

"We want everyone to know the importance of this event, given the possible involvement of organized crime," he said.

Even if it was a drug attack, Mexico is still a long way from the kind of drug violence that rocked Colombia in the late 1980s, when cocaine barons bombed an airliner to try to halt extraditions to the United States.

'SUBVERSIVES' NOT LIKELY TO BLAME

But Calderon has received threats for sending 25,000 troops against the cartels and the smugglers are growing bolder, killing local politicians and staging fierce shootouts with troops in broad daylight.

The attorney general's office appeared to rule out the left-wing Popular Revolutionary Army, EPR, as authors of Friday's bombing in a busy neighborhood popular with tourists.

The rebels blew up oil and gas pipelines last year in attacks that crippled industry but killed no one.

"Given the information we have at the moment, the methods and characteristics of the explosives suggest this is not attributable to armed or subversive groups," the office said in a statement.

A spokesman for the attorney general's office said it was too early to know who carried out the bombing.

The Sinaloa's main enemy is the powerful Gulf Cartel in the northeastern state of Tamaulipas, near Texas, and a person close to the cartel said the Gulf gang was unlikely to have taken part, blaming their Sinaloan enemies.

"From the way it happened and where it took place, you cannot pin responsibility on the Gulf Cartel," the source told Reuters. He said those most hurt by the government's drug offensive have been Guzman's people, including a recent arrest made by the Public Security Ministry.

Police in Mexico City, one of the world's biggest urban areas with a population of 18 million, promised a major increase in security after the blast. (Additional reporting by Adriana Barrera in Mexico City and Magdiel Hernandez in Nuevo Laredo; editing by Doina Chiacu)

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