HAVANA, March 19  -- The Revolutionary Armed Forces of Colombia (FARC) rebel group Thursday called on President Juan Manuel Santos to "save" a unilateral and indefinite ceasefire the guerrillas decreed in December, which was being "undermined" by military attacks.

"We ask President Santos to do something to save the truce ... and to stop these operations against the guerrilla forces," rebel spokesman Ivan Marquez told reporters in Havana, where the two sides in the five-decade conflict are holding peace talks.

Marquez said the rebel group was concerned to see "how the attacks have progressively undermined the FARC's determination to maintain a unilateral and indefinite ceasefire."

The attacks "aim to scuttle" the peace talks by flaring up violence when negotiations enter a new round, said Marquez.

"Please, do not force us to break our determination," Marquez said.

The government delegation to the talks issued no statement to the press upon arriving at Havana's convention center, which has hosted the negotiations since they began in November 2012.

Santos last week announced the military would stop bombing rebel strongholds for a month as a step toward the "de-escalation" of the conflict.

The Colombian conflict, the longest-running civil conflict in Latin America, has left 220,000 people dead and displaced more than 5 million people, according to official figures.