Colombia's President Juan Manuel Santos said Friday FARC rebels would keep their weapons until a peace agreement is ratified, but a ceasefire will begin immediately a deal is agreed.

Santos laid out the sequence he envisions for ending Colombia's half-century-long armed conflict as negotiators in Havana plod slowly toward an agreement.

The sides have reached agreement on only one of five agenda points since the talks started in November, but Santos has been pressing for swifter movement toward a final accord.

"As soon as we reach some agreement, there is an immediate ceasefire, and we enter the third phase, that of implementation," Santos said in an interview with Blu Radio.

"And one of the fundamental steps is that the people will be able to express themselves, to put it to a referendum," Santos said.

Santos said the surrender of weapons by the rebels would come after a referendum.

"This is still to be negotiated, but in practice the handover of arms, that the arms belonging to the FARC are set down, you can be absolutely sure of because it is part of the process," he said.

Santos surprised the FARC last month by introducing legislation that would require any peace agreement to be put to a national referendum.

The FARC has opposed the proposal, arguing instead for the formation of constituent assembly to give legal standing to a peace agreement.

Negotiators in Havana have reached agreement only on how to deal with issues of rural development.

They have also begun discussions of conditions for the FARC's reintegration in the country's political life, but have yet to take up three other issues: the surrender of weapons, compensation for victims of the conflict, and drug trafficking.

The leftist rebel group, the country's largest, took up arms against the state in 1964 in what has become the longest running conflict in Latin America.