Colombia's FARC rebels have killed seven soldiers and injured five others in the worst violence against security forces since peace talks began late last year, the army said in a statement.
An unidentified number of the rebels were also killed in the fighting in southern Caqueta province.
The violence came just hours before two captive police officers were due to be released by FARC, or Revolutionary Armed Forces of Colombia, which has been holding them since last month.
The army is planning a brief ceasefire in two southwestern states to facilitate their release.
Fighting has intensified in recent weeks as FARC steps up pressure on the government while the two sides seek a negotiated end to five decades of war in talks in Cuba.
They had reported progress earlier this week on negotiating the key issue of land redistribution.
The Marxist group lifted a unilateral ceasefire on January 20 and have increased attacks on civilian and military targets, taken hostages and blown up oil and energy infrastructure in a bid to force the government to suspend hostilities.
On Tuesday, suspected FARC fighters killed a policeman and a boy and wounded 27 other people, many of them children, in a grenade and gunfire attack in the southern province of Guaviare.
Colombian president Juan Manuela Santos has said the military offensive will end only if peace is reached.
While US-backed strikes against FARC have severely weakened the rebels and limited their ability to attack the country's economic drivers, the FARC is still able to put up a fight with the military.