At least 21 people were killed and dozens injured in a car bomb blast at a police academy in Colombia's capital, Bogotá, on Thursday morning, according to officials, who called it a terrorist act.

Columbia's defense minister blamed the attack on a leftist rebel group called the National Liberation Army, or ELN, which has carried out occasional attacks in the country. The bombing has stoked anxiety about a return to the decades when innocent Colombians got caught up in conflicts with rebel groups and drug cartels.

Chaos pierced the calm Thursday when a man drove up to the gates of the Escuela General Santander around 9:30 a.m. local time, according to local news reports. He accelerated, crashing into a wall. Then the explosion went off, NPR reports.

Chief Prosecutor Néstor Martínez identified the attacker as José Aldemar Rojas, an ELN operative who had previously lost an arm in an explosives accident, according to The Associated Press. He was allegedly driving a 1993 Nissan SUV loaded with 175 pounds of pentolite, a highly explosive material.

Colombia's Health Ministry said 35 people were wounded in the blast. Other sources put the number at 54.