Colombian rebels have ambushed a team of security force personnel, killing 17 soldiers and secret police officers in one of the deadliest attacks this year.
Rebels opened fire and detonated roadside explosives as the troops drove through mountains near the Venezuelan border, an army statement said.
The ambush is being blamed on two left-wing groups.
Observers fear guerrillas are stepping up attacks in advance of the presidential election in May.
The ambush happened near the town of Hacari in Norte de Santander province, some 400km (260 miles) north-east of the capital, Bogota.
It is close to the border with Venezuela and is one of Colombia's most violent areas.
A soldier wounded in the ambush said the rebels began by opening fire and then blowing up the vehicle.
"We were on the road when we saw the guerrillas on the hillside above us. They had the ambush ready," he was quoted by Reuters as saying.
The dead included 11 agents from the Administrative Security Department (DAS)and six soldiers.
The commander of the Colombian army, Mario Montoya, said they were attacked by fighters from two guerrilla groups - the Revolutionary Armed Forces of Colombia (Farc) and the People's Liberation Army (EPL).
Violence has increased ahead of the presidential election due on 28 May.
Two weeks ago, 15 soldiers were killed in clashes with Farc rebels, including 12 in a single ambush.