Fighting in an area key to drug trafficking in southeastern Colombia left at least nine rebels from the National Liberation Army (ELN) and one Marine dead, the country's navy said on Monday.
The clashes took place last weekend in jungle terrain close to the Pacific port city of Buenaventura, just two weeks before peace talks between the government and the ELN are set to continue in Mexico.
Colombia has endured almost six decades of internal armed conflict, which has left at least 450,000 dead and millions displaced.
The government concluded a preliminary round of talks with the ELN in Venezuela last year and held an emergency meeting this month to overcome a communications issue regarding a potential ceasefire.
President Gustavo Petro, Colombia's first leftist leader, has promised to seek peace deals or surrender agreements with all the country's illegal armed groups.