A powerful car bomb explosion rocked a northern district of Colombia's capital on Thursday, injuring at least nine people and causing extensive damage, authorities said. 'Fortunately we do not have anybody dead,' national police chief Oscar Naranjo told reporters at the scene, the first major attack since President Juan Manuel Santos' weekend inauguration. 'It's a terrorist act... I believe this is a message, this is not gratuitous,' Santos said at the scene, without specifying who he thought was behind the incident. Preliminary investigation found that the early morning attack involved some 50 kg of explosives loaded in a Chevrolet car, according to police. Bogota police commander Cesar Pinzon said some of the injured suffered minor injuries on their faces or arms. Several of the injured were on a bus that was passing when the car bomb went off near Caracol Radio, a popular private radio station named Caracol Radio. Health Secretary Hector Zambrano said at least nine people were injured. Most of the injured were treated for cuts but three remained under care, he said. The building housing the radio station was evacuated after part of its roof collapsed, Caracol employees said. Local TV footage also showed that windows in nearby buildings were shattered and some vehicles were damaged. Similar attacks have dropped sharply since Santos' predecessor Alvaro Uribe took office in 2002. When taking office on Saturday, Santos vowed to continue the war against guerrillas of the Revolutionary Armed Forces of Colombia (FARC) and drug- traffickers. 