The Colombian government has released a jailed guerrilla leader in the hope he will encourage the rebels to release the 56 hostages they hold.
Rodrigo Granda was captured in Venezuela in 2004
Rodrigo Granda, known as the Farc rebel group's "foreign minister", was freed as the authorities prepare to release up to 200 guerrillas from prison.
Colombian President Alvaro Uribe said French President Nicolas Sarkozy had pushed for Mr Granda's release.
Among the hostages is French-Colombian politician, Ingrid Betancourt.
Mr Granda was flown by helicopter from the prison grounds to the Colombian capital, Bogota, where he was taken to the offices of the Roman Catholic archbishop.
His release was less dramatic than his capture in Venezuela in 2004, when he was smuggled across the border into Colombia in an incident that led to a breakdown in relations with Venezuelan President Hugo Chavez.
Mr Uribe announced the rebel leader's release in a TV and radio address.
"The government has guaranteed his safe passage so that he may promote peace," Mr Uribe said.
The Colombian president said that Mr Granda was released at the request of Mr Sarkozy.
In a statement on Tuesday, Mr Sarkozy welcomed Mr Uribe's "very important and courageous decision" and expressed the hope that the Farc would respond.
Ingrid Betancourt's fate has been closely followed in France
The French authorities have been pushing for the release of Ms Betancourt, a former Colombian presidential candidate who also has French citizenship.
She was kidnapped more than five years ago.
President Uribe, who had previously announced that he would release up to 200 jailed rebels as part of a unilateral goodwill gesture, said the first 50 prisoners would be freed on Tuesday after they had officially demobilised and promised not to return to crime.
Mr Uribe is hoping that Farc will reciprocate the gesture by releasing the hostages they hold.
The guerrillas have yet to respond specifically to the release of Mr Granda, but in a communique over the weekend the group called the government gesture a farce.
Most of the prisoners due to be released were Farc deserters or civilians mistaken for rebels, they said.
They said they would discuss the possibilities of a prisoner exchange if and when the government granted a safe haven as a venue for talks - a request repeatedly rejected by Mr Uribe.
"I cannot accept a demilitarised zone but I also cannot stop seeking the release of my compatriots and the three kidnapped Americans," Mr Uribe said, referring to US citizens kidnapped in 2003.