BOGOTA (Reuters) - Seven people were killed and 11 more injured when a passenger vehicle exploded while traveling down a highway in southeast Colombia, in a key drug-trafficking region where illegal armed groups vie for control, a high-ranking military official said on Tuesday.

The explosion, which is being investigated by authorities, happened late on Monday in a rural region of Colombia’s Cauca province, some 500 kilometers (300 miles) southeast of capital city Bogota.

“This was no attack. This was a passenger vehicle moving from Pasto toward Cali. It was moving when it exploded,” General Jorge Isaacs Hoyos, commander of the Colombian army’s third division, told journalists.

Those who died were thrown from the vehicle when it exploded, the general said. The explosion hit two other vehicles and forced them from the road, injuring those inside, Hoyos said.

The region where the explosion happened is contested by guerillas of the National Liberation Army (ELN), dissidents of the Revolutionary Armed Forces of Colombia (FARC) - who returned to arms citing a breakdown of the 2016 peace deal - and criminal groups connected to drug trafficking, according to security sources.

The cultivation of coca leaves and the production of cocaine fuels conflict in the Andean country, which after more than 50 years has left 260,000 dead and millions displaced, according to the government.

The explosion happened following an escalation in attacks by the ELN in different regions of the country, where the rebels have set fire to vehicles, blocked roads, threatened citizens and attacked army patrols.

(This story corrects headline and paragraphs one and three to say that the vehicle that exploded was a passenger vehicle not a military vehicle. Also corrects quote in paragraph three to say “This was no attack” from “This was no random attack.”)