President Juan Manuel Santos, frustrated over a lack of progress in peace negotiations with leftist FARC rebels, threatened Saturday to abandon bilateral talks to end their nearly 50-year old conflict.

"As long as we make progress we'll be satisfied, but if we do not make progress we'll leave the negotiating table," Santos said at a public event in the town of Santa Barbara, in the northwestern department of Antioquia.

Rebels with the Revolutionary Armed Forces of Colombia (FARC) and the Santos administration opened peace talks in Norway in October, and continued them in second-round talks that began in Cuba the following month.

The FARC declared a two-month unilateral ceasefire after the talks opened, but did not extend it after the government failed to reciprocate.

"The rules of the game are very clear," Santos said Saturday.

"There is no ceasefire of any kind, neither military nor judicial, nor even verbal. These are the conditions that we set from the beginning."

The two sides, which have been in conflict since 1964, are holding talks on the thorny issue of land reform, which tops a five-point peace process agenda.

Talks are being held on four additional points: the surrender of weapons by the rebels; turning the FARC into a political party; the illegal drug trade; and reparations for victims of the conflict.

The last attempt at a settlement collapsed in 2002 when rebels used a Switzerland-sized demilitarized zone set aside as an encouragement for peace to regroup and rearm.

FARC leader Timoleon Jimenez urged Santos in a letter posted on the rebel's website on Friday to prevent the talks from "sinking in a swamp" as a result of the government's "official actions."

FARC negotiators also called on officials in Bogota to form a joint commission to interview peasants displaced by the conflict, to try to determine who is responsible for their plight.

The FARC accused Santos of leading a "mendacious media campaign" that blames the the rebels for pushing peasants off their land, in a bid to avoid talks on agrarian reform.

The five-decade-long conflict has dislodged some 3.7 million people in Colombia, one the highest number of internally displaced people in the world. Thousands of other Colombians have fled the country, especially to neighboring Panama.

The FARC, with some 8,000 fighters in arms, emerged in the 1960s in response to a yawning wealth gap between Colombian peasants and wealthy owners of huge haciendas, or estates.

Colombia's unrest, which also involves a second leftist rebel group, the ELN, short for Ejercito de Liberacion Nacional or National Liberation Army.

The discussions also encompass Colombia's right-wing paramilitaries, drug traffickers and the government forces attempting to impose order.