The remains of a vehicle used in a car bombing are cordoned off in a street in the northern border city of Ciudad Juarez, Mexico on Friday. ((Associated Press)) A drug cartel has used a car bomb for the first time in Mexico's decades-long fight against traffickers, setting a deadly trap for federal police, the mayor of Ciudad Juarez said Friday.

Jose Reyes said federal police have confirmed to him that a car bomb was used in the attack that killed three people Thursday.

It was the first time a drug cartel has used a bomb to attack Mexican security forces, marking an escalation in the country's already raging drug war.

Federal police and paramedics were lured to the scene by a phone call reporting that shots had been fired at a major intersection and a municipal police officer lay wounded at a major intersection, Reyes told The Associated Press.

As the paramedics were working on the wounded man, a parked car exploded, he said.

Reyes said authorities later determined that the wounded man was not a policeman, but a man wearing a fake uniform. The man was among the three people killed in the attack. The others were a federal police officer and a medical technician.

Brig.-Gen. Eduardo Zarate, the commander of the regional military zone, told reporters that up to 10 kilograms of explosives might have been used, although investigators were still trying to determine what type.

He said the bomb might have been detonated remotely with a cellphone, adding that burned batteries connecting to a mobile phone were found at the scene.

"From what distance? We don't know. But we think it was a distance that allowed [the assailants] to watch the area, waiting for the police to get out of their vehicle," Zarate said.

Growing boldness

The car bomb demonstrates the growing boldness and military sophistication of Mexico's drug traffickers, who have dramatically stepped up attacks against security forces and government officials since President Felipe Calderon deployed thousands of troops and federal police to crush the cartels in their strongholds.

"We have to change the way we operate," Reyes said. "We've started changing all our protocols to include bomb situations."

City and federal authorities said the attack appeared to target only security forces.

"The threat was directed at the police departments, so it is not a threat against the population," he added. "But we have to be very careful with our police departments, their actions and how we protect them, and of course, how we protect the population from the fallout."

A graffiti message appeared on a wall of a Ciudad Juarez shopping mall on Thursday night warning of more car bombs.