The top negotiator for Colombia's leftist FARC rebel group said Monday he was confident that the nearly 50 year old guerrilla war is almost over.

"We understand, and the country understands it as well, that wars are not eternal, and we feel certain somehow that Colombia is near the end of the conflict," Ivan Marquez said in a radio interview.

Marquez is the FARC's number two and the rebel group's lead negotiator in peace talks with the government that have been underway in Havana since November.

"If artificial impediments are not put in the way, this will flow quickly," he said in the interview with RCN radio.

Asked whether a peace agreement could be signed by next November, as Colombian President Juan Manuel Santos has urged, Marquez said, "It's possible, but I wouldn't go so far as to assert it."

Negotiators have reached agreement on the top item on the agenda, which concerns rural development. Starting Monday, they are to begin discussing the question of the rebels' participation in politics.

Other agenda items include drug trafficking, the surrender of weapons and reparations for victims of the conflict.

Marquez said a constituent assembly should be convened to make the institutional changes needed to provide a foundation for peace.

Such a constitutional assembly "would surround the (peace) agreement with legitimacy," he said.

"No successor president would be able to say, 'I do not recognize these agreements.' It is very important for that reason," he said.

Santos' term ends in August 2014, although he could run for reelection.

The FARC has not said how it intends to re-engage in politics once a peace agreement is reached, but Marquez indicated that the FARC would seek to form a coalition of leftist forces.

Formed in 1964, the Revolutionary Armed Forces of Colombia, or FARC by its Spanish acronym, is the country's largest guerrilla group, with an estimated 8,000 fighters.

A smaller leftist guerrilla group, the National Liberation Army, or ELN, is also active in Colombia and has so far remained outside the peace process.

Marquez said it was up to the government and the ELN to decide what their next steps will be.

"They will surely reach an agreement on how to engage in talks. If the ELN thinks it can add to the efforts at the negotiating table in Havana, for our part we would have no problem with it," he said.