CIUDAD JUAREZ, Mexico – A drug cartel has used a car bomb for the first time in Mexico’s decades-long fight against traffickers, setting a deadly trap against federal police in a city across the border from Texas, the mayor of Ciudad Juarez said Friday.

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

It was the first time that drug cartels have used explosives 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 a municipal police officer lay wounded at a major intersection, Reyes said.

As 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, although he was wearing a fake uniform.

The man was among the three people who died in the attack. The others were a federal police officer and a medical technician.

Brig. Gen. Eduardo Zarate, commander of the regional military zone, told reporters that up to 10 kilograms of explosives might have been used, and that the bomb might have been detonated remotely with a cell phone. He said investigators were still trying to determine the type of explosive used.

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.

In the northeastern border city of Nuevo Laredo, a series of shootouts Friday prompted the U.S. Consulate to warn American citizens in the city to remain indoors. The consulate said drug traffickers were throwing up roadblocks in at least one major avenue and were carjacking vehicles.

“We have received credible reports of widespread violence occurring now between narcotics trafficking organizations and the Mexican Army in Nuevo Laredo. We have credible reports of grenades being used,” the consulate said in a statement.

“We advise all U.S. citizens in Nuevo Laredo to remain indoors until the security situation improves.”