Bogota, Sept 20 (Xinhua-RHC), -- Two guerrilla rebels and a policeman were killed when an unidentified group of insurgents were trying to launch an explosive on a police station in the northwestern Colombian city of Arauca on Friday.

Colombia's Caracol Radio network quoted a police report as saying that the insurgents sought to launch an explosive, but police officers reacted in time and shot dead the two guerrilla rebels who were on a motorcycle.

The incident took place just a few kilometers away from the Colombian border with Venezuela. An investigation is underway to determine which insurgent group is responsible for the attack.

According to authorities, it is still unknown which rebel group had plotted the attack because in the area there is a high presence of the two largest guerrilla groups in Colombia -- the National Liberation Army (ELN) and the Revolutionary Armed Forces of Colombia (FARC).