Bogota (AFP) - Colombia released 16 FARC guerrillas Thursday, the first to walk free under a pardon issued in peace negotiations that appear to be closing in on a deal to end a half-century conflict.

The jailed rebels, the first out of a group of 30 to be pardoned, were released in a goodwill gesture to reciprocate for a unilateral ceasefire declared six months ago by the Revolutionary Armed Forces of Colombia (FARC), said the office of the government's high commissioner for peace.

"This is a first, unilateral gesture by the government after evaluating the observance of the FARC's unilateral ceasefire and the resulting reduction in violence and advances in the (peace) process," it said in a statement.

The FARC welcomed the release as a "positive gesture," but called on the government to also free 80 other rebels with health problems.

The newly freed inmates themselves insisted the move was only a first step.

"We still can't break into applause, because our comrades are still in prison," Sandra Patricia Isaza, one of those freed, told journalists.

The jailed guerrillas were serving sentences for rebellion, a catch-all charge against FARC members. They had not been convicted of serious crimes.

President Juan Manuel Santos's government pardoned them on November 22.

Under the terms of their release, the rebels -- nine men and seven women freed from two Bogota prisons -- must promise not to re-enter the FARC.

But four of them will be allowed to travel to the three-year-old peace talks in Havana, where they will be briefed as "authorized civilians," the government said.

- Getting to know FARC -

Political analyst Jorge Restrepo called the release a key "trust-building gesture" as negotiators seek to chart a post-conflict future in which the FARC will transition from a guerrilla group to a political party.

"For the first time, we will see the FARC acting in society. We will see who they are, what they're going to do and whether they will participate in politics," he told AFP.

Story continues

The peace talks in Havana have made several key advances in recent months, and the two sides have set a deadline of March 23 to sign a final accord -- though the FARC have warned that "substantial" obstacles could get in the way.

The two sides have signed deals on four of the six agenda items at the talks: justice for victims, land reform, political participation for ex-rebels and fighting the drug trafficking that has fueled the conflict in the world's largest cocaine-producing country.

The unsettled issues are disarmament and the mechanism by which the final accord will be ratified.

The two sides opened talks Thursday on dealing with right-wing paramilitary groups that the FARC say are still killing rebels and assassinating leftist leaders despite being officially disbanded.

Negotiators announced Tuesday that they have asked the United Nations to send an unarmed observer mission to monitor the eventual end of the conflict and oversee the disarmament of the FARC.

The Colombian conflict, which has killed more than 220,000 people and displaced six million, has drawn in right-wing paramilitaries, drug traffickers and several leftist rebel groups, of which the FARC is the oldest and largest remaining.

A rival rebel group, the National Liberation Army (ELN), has held exploratory talks with the government but has yet to join the peace process.