Colombia's FARC guerrillas acknowledged Monday they are holding a soldier captive, setting up a possible standoff with the government as they try to close in on a peace deal.

The rebel group, which has been observing a unilateral ceasefire since July, said it captured Jesus Rojas as he "carried out a combat intelligence mission" in southwest Colombia.

The army, which announced Rojas's capture last week, said he was kidnapped while on leave. But the rebels said he was traveling in disguise as a truck driver's assistant to spy on a rebel stronghold in Caqueta department.

Defense Minister Luis Carlos Villegas has called on the Marxist rebels to free the soldier as a goodwill gesture for Christmas.

The FARC said Monday it was "willing" to release him, but did not give further details. It called for help from the Red Cross, which has facilitated the release of rebel captives in the past.

The rebels say that under their ceasefire, they take only defensive actions to protect themselves.

The government and FARC have been holding peace talks in the Cuban capital Havana for the past three years.

They have signed partial deals on several issues, but have yet to reach a definitive peace accord to end a five-decade conflict that has killed more than 220,000 people.

Both sides have vowed to reach a final deal by the end of March.

Founded in 1964, the Revolutionary Armed Forces of Colombia (FARC) today has an estimated 7,000 fighters.