War-weary Colombia celebrated Monday the start of a FARC rebel ceasefire after a half-century of hostilities, with hopes still high that its fragile peace process can hold.

Marxist FARC guerrillas freed a captive soldier Sunday in an apparent goodwill gesture hours before they started observing the unilateral ceasefire.

FARC guerrillas on Sunday freed a Colombian soldier after holding him for nearly two weeks, the president said, on the eve of a unilateral rebel ceasefire.

Lieutenant Cristian Moscoso "is free and in good condition," President Juan Manuel Santos wrote on Twitter, following an International Committee of the Red Cross humanitarian operation.

The Colombian government reached a historic agreement Sunday with leftist FARC guerrillas to de-escalate the decades-long armed conflict, diplomats in Havana said.

The move marks a significant step in peace talks between the two sides that began in November 2012 but have been hampered in recent months by an uptick in violence.

Fighting between Colombian troops and leftist FARC guerrillas left two soldiers dead and three wounded, the latest casualties in an uptick in violence, officials said Friday.

The skirmish erupted in the western Cauca department when the FARC, who are holding captive a wounded military officer, detonated an explosive device.

Colombia's leftist FARC rebels announced Wednesday they will observe a one-month unilateral ceasefire in response to an international appeal for an urgent de-escalation in the country's decades-old conflict.

The truce will start July 20, said Ivan Marquez, chief rebel negotiator at long-running peace talks in Havana.

Four countries supporting peace talks between the Colombian government and FARC rebels called Tuesday for an "urgent de-escalation" of armed conflict in the South American nation.

The appeal comes after armed clashes resumed in mid-April, following an ambush by the Revolutionary Armed Forces of Colombia (FARC) that left 11 soldiers dead. Each side blames the other for the escalation.

President Juan Manuel Santos has replaced Colombia's top military leaders, days after the release of a Human Rights Watch report alleging complicity by the country's top brass in extrajudicial killings of civilians.

In a press conference Monday, Maduro announced that General Jaime Alfonso Lasprilla, head of Colombia's army, would be replaced by General Alberto Mejia Ferrero.

More than a million faithful -- some of whom traveled for hours and spent the night outdoors -- gathered Monday for the first open-air mass of Pope Francis's three-nation trip to South America.

Keeping vigil in tents, sleeping bags and on cardboard, tens of thousands hoping to catch a glimpse of the pontiff spent the night in the rough ahead of the service in Guayaquil, Ecuador's largest city.

The Colombian government is ready to consider a bilateral ceasefire with FARC rebels, even before the end of peace talks, the country's chief negotiator said in an interview released Sunday.

The statement marks a sharp reversal for Colombia, which had previously refused to consider a halt to fighting until the negotiations had succeeded.

At least 10 people were hurt when two minor blasts rattled the Colombian capital Bogota on Thursday, officials said, putting authorities on alert amid an uptick in violence.

The first blast hit in the financial heart of Bogota at about 3:45 pm (2045 GMT), the fire department said on Twitter, reporting a second explosion moments later at an industrial area.