Colombia's FARC negotiator Ivan Marquez arrives for talks in Havana, Cuba.

Havana - Colombia's FARC rebels said on Monday they would call a two-month unilateral ceasefire, the first truce in more than a decade, as peace negotiators met in Cuba in the latest attempt to end the five-decade war.

President Juan Manuel Santos' government, however, has so far rejected any stoppage of military operations until a final peace deal was signed with the Revolutionary Armed Forces of Colombia, or FARC, and even vowed to step up the offensive.

The FARC said it would halt all offensive military operations and acts of sabotage against infrastructure beginning at midnight on Monday night and running through January 20.

“This policy decision of the FARC is a contribution made to strengthen the climate of understanding necessary so that the parties that are starting the dialogue achieve the purpose desired by all Colombians,” FARC lead negotiator Ivan Marquez said as he arrived for talks in Havana.

The gesture is a positive sign that the rebels are keen to push talks forward to a successful end, something that was thrown into doubt by long, drawn out speeches by its leadership calling for major changes to Colombia's political system.

Delegations for the government and the FARC arrived in black luxury cars at Havana's convention centre where they will meet almost daily until the talks end.

The complex is located in Havana's plushest neighbourhood, filled with palatial houses that once belonged to the elite, virtually all of whom fled Cuba after the 1959 revolution.

Colombian government negotiators did not speak upon arrival.

The war has dragged on for nearly half a century, taking thousands of lives, displacing millions more and causing damage to infrastructure in Latin America's longest running insurgency.

Failure of the peace process would mean years more of fighting and further blight on the reputation of a country eager for more foreign investment and regional clout, yet which has been unable to resolve its most serious domestic problem.

The announcement by the FARC would be a breather for oil and mining companies, the target of many FARC attacks in recent months as the group seeks to hobble Santos's main source of international revenue.

Colombia's conflict proved to be intractable in three previous peace processes, but both the government and the FARC have expressed optimism that this time might be different.

Santos wants an agreement within nine months, although the two sides face plenty of thorny issues in their five-point agenda, which will begin with rural development.

The other four points are the political and legal future of the rebels, a definitive end to the conflict, the problem of drug trafficking and compensation for war victims.

“You have to take this announcement with a grain of salt,” Felix Lafaurie, head of the National Federation of Cattle Ranchers, said on local radio.

“I hope this is going to be a sign of the FARC's good will and not that they're then going to take swipes on substantive issues.”

The conflict dates back to 1964 when the FARC emerged as a communist agrarian movement intent on overturning Colombia's long history of social inequality.

The group has been weakened by a US-backed military offensive started in 2002 that has reduced its numbers to about 8 000 and forced them into remote mountain and jungle hideouts.

But it still has the strength to launch attacks that Santos wants ended so the country can grow its economy, boosted in recent years by fast-growing oil and mining sectors.

The FARC has sustained itself by cocaine trafficking, kidnapping, ransom and “war taxes” charged within the territories it controls.

Its leaders deny involvement in the drug trade and renounced kidnappings earlier this year, but the United States and European Union consider it a terrorist organisation.

Officials want the talks held in the strictest possible secrecy, which is likely the reason they are in Cuba, where the government is expert at keeping information close to the vest.

Venezuela and Chile also will have representatives there. - Reuters