Colombia's main leftist rebel group has ambushed and killed eight soldiers in its second deadly attack in the south in two days, the military says.
The Iscuande post was hit by home-made rockets
A civilian also died and four soldiers were injured as Farc rebels reportedly set off mines on a bridge in Putumayo province as a patrol crossed.
The news came as officials gave more details on Tuesday's strike on a military outpost, which killed 15.
Meanwhile Venezuela denied Farc rebels were passing through its territory.
Vice-President Jose Vicente Rangel told the BBC he had no reason to believe, either, that they had camps inside Venezuela.
President Hugo Chavez and his Colombian counterpart Alvaro Uribe plan to meet on Thursday in the hope of settling issues outstanding after a recent diplomatic row.
The dispute was triggered by the kidnap and abduction of senior Farc (Revolutionary Armed Forces of Colombia) official Rodrigo Granda from Venezuela by bounty-hunters acting on behalf of Colombia.
Battle for control
The attacks in southern Colombia suggest the Farc rebels retain the capability of striking against the government despite its offensive, called Plan Patriot.
Describing Tuesday's attack in the village of Iscuande, Narino province, local mayor Jose Maria Estupinan said the rebels launched home-made rockets at the military outpost.
At least 25 troops were wounded in the fighting, which officials now say was part of a struggle for control of a river used by cocaine traffickers.
The area where the Iscuande River empties into the Pacific Ocean in Narino is known as a major cocaine-producing centre.
Among those attacked were campesino, or peasant, marines, natives of the area who are stationed at local military posts after a short period of training.
Their deployment forms a major part of President Alvaro Uribe's strategy to end a 40-year insurgency by members of the Farc to an end.
The Colombian authorities say the army has discovered what it says is a huge stockpile of armaments belonging to the Farc.
Reports say Colombian troops made the discovery in the southern jungle region of Guaviare four days ago, but waited until Wednesday to report it.
The US has provided about $3bn (£1.6bn) in mostly military aid to Colombia since 2000 to combat both the rebels and the country's huge cocaine industry.