President Juan Manuel Santos on Sunday warned Colombia's Marxist FARC rebels they have less than a year to strike a deal under recently opened peace talks aimed at ending Latin America's longest-running insurgency.

"This has to be a process of months, rather than years. In other words, this should not last any longer than November next year at the latest," the president said at an event in the Caribbean resort city of Cartagena.

"But it is important to be patient, and not demand immediate results, because... some very complicated issues are being discussed."

The Revolutionary Armed Forces of Colombia (FARC), Latin America's longest insurgency, started talks formally with Bogota on October 18 in neutral Norway. The talks moved to Havana on November 19 and will resume this week.

It is a conflict that has dragged on for almost a half century, with some 600,000 dead, 15,000 missing and four million people domestically displaced.

Last Thursday, Colombian government and rebel negotiators reported progress in the first peace talks in a decade, as they try to end Latin America's longest running guerrilla insurgency.

On the delicate process of the FARC making a transition to a civilian political force, Santos said his government would agree to them trading bullets for ballots as long as they were not "politicking with their firearms."

"If the FARC indeed wants to end the conflict and move from bullets to the ballot box, take part in politics and seek to achieve goals in democratic processes, they will find the government most willing and cooperative," he said.

"But if what they are seeking is once again to put their revolution by decree on the table, over there in Cuba, and change the Constitution and the country and its public policy, there won't be any peace there," he warned.

Talks are to resume on Wednesday, and will continue to focus on land reform, the first point on the agenda, the parties said in a joint statement.

Ivan Marquez, the FARC's number two negotiator, has said an agreement reached to hold a public forum in Bogota next month on agrarian development -- unequal land distribution is a longstanding problem at the root of the conflict -- was the best sign the process is moving forward.

Previous attempts at peace have failed. In the last effort, which lasted from 1999 to 2002, the government ended talks after concluding the FARC were using a vast demilitarized zone to regroup.

The FARC -- founded in 1964 and believed to have some 9,000 armed fighters -- took up arms to protest against the concentration of land ownership in Colombia.

The rebels have suffered a string of military defeats in recent years, and several of their top commanders have been captured or killed. FARC ranks have also been severely depleted from its peak in the 1990s.

Aside from reaching a deal on land ownership, both sides must also agree on a mechanism to end hostilities, incorporating the FARC into political life, curbing drug trafficking, and on compensating victims of the conflict.