Bogota (AFP) - President Juan Manuel Santos declared Colombia's 50-year conflict with FARC guerrillas finally over on Tuesday, as the last truckloads of decommissioned weapons rolled away to be melted down.

Santos himself shut a padlock on the last lot of decommissioned rifles before it was taken out of a remote demobilization camp to formally seal the UN-supervised disarmament by the Revolutionary Armed Forces of Colombia (FARC).

"With the laying down of arms ... the conflict is truly over and a new phase begins in the life of our nation," Santos said at a ceremony in Pondores, a remote area in the northern Guajira department.

"This is truly a historic moment for the country," he said.

"We have been a republic for 198 years. Never had we had such a long conflict and today is indeed the last breath of that conflict."

The leftist rebel force has said it will officially transform into a political party on September 1, a major step in reintegrating into civilian life as part of a historic peace deal signed last year.

"Soon we will be holding a founding congress for the new political party that will be called the Alternative Revolutionary Force of Colombia," said one of the FARC's senior leaders, Ivan Marquez, at Tuesday's ceremony.

"We do not want to break with our past. We were and will continue to be a revolutionary force," said Marquez.

The FARC arose in May 1964 from a peasants' revolt, and its ranks were made up mostly of country-dwellers who rallied behind the group's Marxist-Leninist ideology, with land reform its key demand.

As well as a quarter of a million dead, about 60,000 Colombians remain unaccounted for and seven million have been displaced in the conflict.

A small rebel group called the National Liberation Army is now in peace talks with the government. And 450 renegade FARC members are refusing to embrace the idea of peace.

For now, former FARC rebels will live in 26 demobilization camps.

On Tuesday the group also brought out 24 minors who were child soldiers still under the protection of the FARC. They joined another 88 who were already turned over to the government, the International Committee of the Red Cross said.

- Uncertain future -

So far, 88 such minors have been turned over to the authorities.

Amid the sense of exhausted relief that many Colombians feel after so much war, the road ahead is fraught with challenges.

One issue is how to ensure the physical safety of former rebel fighters, who many Colombians feel are getting off too easy. Marquez said two former rebels have been murdered in recent days.

Another, even bigger problem is how the former fighters will make a living.

"The guerrillas do not know what is going to happen to them the day after tomorrow," said Ariel Avila, director of a foundation that is monitoring the peace accord.

Then there is there is the issue of justice for atrocities committed during the war.

The accord calls for non-prison punishment for rebels and soldiers who confess to crimes, pay reparations to victims and pledge to renounce violence forever.