Seven Colombian soldiers have been killed and four wounded in an ambush by left-wing rebels in the south-west of the country, BBC reported.
Rebels from the Revolutionary Armed Forces of Colombia (Farc) launched the attack overnight between Saturday and Sunday, a regional official said.
It came just over a week after the Farc killed eight soldiers in the north-east, near the border with Venezuela.
The attacks are seen evidence that the group is not a spent force.
Fabio Trujillo, a top official in Narino region, confirmed the ambush in the rural district of Samaniego.
An explosive device was set off at almost the same time near the police quarters, wounding two officers, he said.
President Alvaro Uribe condemned the attack.
The Farc has suffered a series of reversals recently, including the death of leader and founder Manuel Marulanda last year.
But the BBC's Jeremy McDermott in Colombia says the rebels appear to be regrouping and retaking the initiative after six years on the back foot.
The new leader, Alfonso Cano, has given the Farc a new vision, he says, directing the rebels towards urban centres and launching more rural ambushes.
Both this weekend's attack and the one in the north-east late last month happened near Colombia's borders.
The rebels are using the border areas as safe havens from which to plan and execute attacks, out of reach of the security forces, our correspondent says.
Narino, near Colombia's border with Ecuador, is also home to the densest concentration of drug crops in the country.
The Farc and other armed groups have profited from the drug trade in Colombia, the world's largest producer of cocaine.
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