Thirteen Colombian marines have been killed and seven wounded after Marxist guerrillas blew up the troops' vehicle by remote control in an ambush on a remote northern highway.
Soldiers fired back and killed five rebel attackers on the road between the towns of Carmen de Bolivar and Zambrano, in Bolivar province, about 330 miles north of the capital Bogota, the army said.
The troops had been escorting a convoy of civilian trucks before the attack by FARC. It was one of the biggest blows for months against Colombia's armed forces, which receive hundreds of millions of dollars of US aid every year.
In a separate operation in Boyaca province 60 miles northeast of Bogota, the army said it captured 34 people suspected of belonging to a far-right paramilitary militia and confiscated a helicopter disguised with air force insignia.
The paramilitaries are fierce illegal enemies of the FARC in a guerrilla war that claims thousands of lives a year.