Colombia's army reported 10 soldiers killed Saturday in an attack blamed on leftist rebels, the second such loss in less than three days.
Ten deaths in a single battle is the heaviest loss by security forces in more than a year, since 14 police officers died in September 2010 when their convoy was attacked in the southern state of Caqueta.
The military blamed both of this week's attacks on the leftist Revolutionary Armed Forces of Colombia.
The army command said Saturday's latest attack happened in a rural area of Tame municipality in Colombia's northeast, about 200 miles (320 kilometers) northeast of Bogota.
The army's announcement gave no details of the fighting. Gen. Jaime Reyes, commander in the region, was reported flying over the area of the attack and did not return calls to his cellphone.
Ten soldiers also died when an army patrol was attacked with mortar fire around midnight Thursday in a rural area near the Pacific port of Tumaco in Colombia's southwest.
The military chief, Gen. Alejandro Nevas, said Friday that "tactical errors" caused those deaths, but the army has not specified what the mistakes were or given details of the fight.
That area is rife with cocaine-smuggling routes to the rugged jungle coast, where traffickers load the drug in semi-submersible vessels for shipment north to Central America and Mexico.
Despite major security gains against rebels over the past decade, they retain the ability to mount hit-and-run attacks, in large part due to Colombia's rugged mountains and thick jungles. Several hundred soldiers and police are killed annually.