The Colombian government has welcomed the announced demobilisation of at least 3,000 fighters from the main right-wing paramilitary group.
The AUC has a northern "safe zone" where they are immune from arrest
The country's peace negotiator described it as a move towards complete disarmament of the United Self-Defence Forces of Colombia (AUC).
The group said its aim was to revive Colombia's flagging peace process.
However the BBC's Jeremy McDermott in Colombia says apparently insurmountable difficulties remain.
The AUC announced on Thursday that it would demobilise 3,000 of its 20,000 fighters by the end of the year.
Government negotiator Luis Carlos Restrepo told reporters he had received the news "with satisfaction and hope".
But he added that a government commission would study the case of each demobilised fighter, and that anyone responsible for committing atrocities or drug smuggling would be jailed.
The AUC has been engaged in talks with the government over the past three months.
However the discussions have been marked by frequent cease-fire violations and suspicions that the paramilitaries have no intention of disarming permanently.
Many AUC leaders are either wanted in the US on drugs charges or accused of serious human rights violations.
The paramilitaries are demanding a total amnesty and immunity from extradition to the US.