Colombia's FARC guerillas have freed a captive soldier in an apparent goodwill gesture, hours before they start observing a unilateral ceasefire.
Colombians who have endured a half-century of bloodshed hope the truce will invigorate a slow-moving peace process, lead to a bilateral ceasefire with the government, and eventually end the war.
It is the last guerilla conflict in Latin America, with 220,000 killed and more than six million people forced from their homes.
The Revolutionary Armed Forces of Colombia announced the month-long truce on July 8, saying it would begin at midnight on Sunday (local time).
With hours to go before the ceasefire, the FARC issued a statement saying its forces should refrain from operations against government forces, and public or private infrastructure.
But in a sign of how fragile the peace process is, the statement said no FARC unit "is obliged to let itself be hit by enemy forces, and will have every right to exercise legitimate defence if attacked".
The FARC also announced the release of a soldier captured nearly two weeks ago during fighting in the south of the country.
The government said he is in good physical condition.
Fitful peace talks have been taking place since 2012 in Havana, but fighting has continued and even intensified this year.
Colombian President Juan Manuel Santos has pledged to negotiate for four more months and then decide whether to continue, but says the truce could be the rebels' last chance.
If they do not live up to the ceasefire, and there is no progress on what kind of punishment would be applied to the rebels under an accord, the peace process will fall apart for good, Santos has said.