Bogota, Colombia ? A bomb set off by suspected rebels Wednesday ripped through a shopping center in northeastern Colombia, killing seven people, injuring at least 20 and setting the complex on fire.

Television images showed shocked survivors wandering around the shopping stalls, blackened Ash Wednesday marks still on their foreheads.

Government officials said the attack in Cucuta, on the border with Venezuela, was part of an attempt by guerrillas to bring the nation’s long-simmering war to Colombia’s cities.

Defense Minister Martha Lucia Ramirez said the urban offensive was a response to government offensives in the countryside. “Unfortunately, that is the risk we have to run,” she said.

Police Gen. Luis Alfredo Rodriguez said the National Liberation Army, or ELN, was responsible for the attack. The bomb was left next to a car in the basement parking lot, police said.

The ELN and the nation’s largest rebel group, the Revolutionary Armed Forces of Colombia, or FARC, are battling outlawed paramilitary groups for control of Cucuta. The city has one of the highest murder rates in Colombia.