By Jeremy McDermott
BBC News, Colombia
The Farc lost their legendary leader Manuel Marulanda in May
Venezuelan President Hugo Chavez' surprise call for the Revolutionary Armed Forces of Colombia (Farc) to end their rebellion and free hostages increases the pressure on the vulnerable rebel army.
The Farc are in a difficult position. The group's legendary leader is dead and it is battered by the US-backed Colombian military in its four-decades-long campaign.
So the call from President Chavez to release the hundreds of hostages they hold comes at a crucial time for the rebels.
The Farc have historically never listened to anyone outside their ranks and proven immune to Colombian public opinion.
Indeed, they have the support of less than 5% of the population.
Yet if there is one man they might listen to, it is Mr Chavez.
Farc communiqués always refer to Mr Chavez and his "Bolivarian Revolution" in the most glowing terms
The Venezuelan leader's "socialism of the 21st Century" is about as close as there is to a working model of what the guerrillas allegedly want to impose in Colombia.
So when Mr Chavez calls for the Farc to release political hostages and sit down to negotiate, Colombia's guerrillas have to take note - Mr Chavez is their principal international friend.
However, in the short term the Farc are unlikely to make a move.
In March the Farc's legendary leader Manuel Marulanda died of what the rebels said was a heart attack.
His successor "Alfonso Cano", a bookish but diehard communist, will need time to consolidate his hold on the rebel group, given that many in the ranks wanted a more ferocious warrior as leader.
What most analysts agree on is that the Farc is unlikely to talk to the Colombian President Alvaro Uribe, whom they hate, and who has been responsible for the series of defeats the rebels have suffered in the last five years.