Ten Colombian troops and 21 right-wing paramilitaries from the United Self-Defence Forces of Colombia (AUC) were killed as they fought on a highway near Villanueva, 325kms east of Bogota.
There are about 10,000 AUC paramilitaries in the South American country. The organisation had been holding peace talks with President Alvaro Uribe's government.
In a separate operation near Llano Grande, 545kms northwest of the capital, a Colombian brigade killed 17 guerillas from the left-wing Revolutionary Armed Forces of Colombia (FARC).
Four government soldiers were also injured in the skirmish.
Colombian troops seized 38 AK-47s, machine guns, grenades and rifles. They also took landmines, unidentified projectiles, radios and military uniforms.
Largest rebel group
Formed in 1966, the 17,000 strong FARC is the largest insurgency in the country.
The rebel army claims to represent the rural poor against Colombia's wealthy classes and opposes US influence in South America.
The organisation operates in about half the country, mostly in the jungles of the southeast and the plains at the base of the Andes mountains.