At least six Colombian soldiers and three leftist rebels were killed when guerrillas attempted an ambush on a military unit in the western department of Choco, officials said.
A patrol was attacked by the "terrorists" of the FARC as it guarded a stretch road near the city of Pretoria on Saturday, a military spokesman told AFP.
Earlier on Saturday, Ivan Marquez, member of the FARC ruling council, warned in a video that the group was not weakened and remained ready to fight, despite overtures of reconciliation that surrounded the landmark release of 10 hostages earlier this month.
The FARC has been at war with the Colombian government since 1964 and is believed to have some 9,000 fighters in mountainous and jungle areas, according to government estimates.
Late March, Colombian troops killed at least 36 suspected FARC rebels and captured four in an army offensive in Meta department, according to officials.