A bombing in the remote Choco department killed the fighters, military sources told AFP, but they were unable to provide more details about the attack.
The government has intensified military operations against the Revolutionary Armed Forces of Colombia (FARC) in recent days even as bilateral peace talks continue in Havana.
So far some 40 rebels have been killed in renewed bombings after President Juan Manuel Santos' ended a government suspension of airstrikes in April following a rebel attack that killed 11 soldiers.
FARC leader Pablo Catatumbo condemned the strikes as a "step backward" as the Marxist group resumed talks in Cuba with the Colombian government Monday.
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Santos rules out any ceasefire before a final peace agreement is reached, but he recently ordered that the names of rebels killed be released, breaking practice with usual government policy.
Founded in 1964, the FARC has some 8,000 fighters mostly in rural areas.
Colombia's internal conflict, which has dragged on for decades, has killed some 220,000 people and left some five million displaced.