The Colombian military says 24 soldiers have been killed in an attack by the country's main left-wing rebel movement FARC.
A defence ministry spokesman said the rebels had used explosives in an ambush by the soldiers.
The soldiers were attacked some 280km southeast of the country's capital, Bogota.
It was the most deadly attack by FARC rebels this year, and part of a campaign of attacks launched by the group since early December on roads in the country's northeast.
On 17 December, FARC fighters killed eight policemen in an attack on a village and held 30 others captive for three days before they were freed.
According to some politicians, the rebels have stepped up their attacks to defend their countryside influence in advance of the coming legislative and presidential elections in 2006.
The 17,000-strong FARC army, together with the nearly 4,500-strong National Liberation Army (ELN), have sought to topple the Colombian government in more than 40 years of civil war that has left more than 200,000 people dead.
