Ten soldiers were killed and six wounded in the deadliest guerrilla attack on Colombia's security forces in more than a year, the army said Friday.
Military chief Gen. Alejandro Navas said "tactical errors" led to the deaths in an apparent ambush around midnight Thursday in the country's turbulent southwest.
In a radio interview, he did not offer details. The local state governor, Antonio Navarro, told The Associated Press the soldiers died in a mortar attack.
Defense Minister Juan Carlos Pinzon told reporters the incident was under investigation.
It occurred near the Pacific port of Tumaco and the dead were part of a 27-man platoon on patrol near an African palm plantation. Killed were a lieutenant and nine enlisted men.
The 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.
Nava said the leftist Revolutionary Armed Forces of Colombia, or FARC, "exploited a weak point, undoubtedly." Military analysts say Colombian troops often leave themselves open to ambush when they linger too long in a given area.
It was the highest death toll for Colombia's security forces in a single attack since 14 police were killed in September 2010 while riding in a convoy in the southern state of Caqueta, a traditional FARC stronghold.
Several hundred security force members are killed annually in Colombia's low-level conflict.
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.
The rebels are to a great degree funded by drug trafficking, as are Colombia's far-right militias, which also operate in the area where Thursday night's attack occurred.