Bogota (Colombia): 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.

Military chief Gen Alejandro Navas said "tactical errors" led to the deaths in an apparent ambush around midnight on Friday in the country's turbulent southwest.

In a radio interview, he did not offer details. The local state governor, Antonio Navarro, told a news agency 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.