Colombian President Alvaro Uribe has opened a conference hoping to secure international aid for a peace process with right-wing AUC paramilitaries.
Alvaro Uribe wants foreign funding
Mr Uribe told delegates that he hoped to establish the process in law with a bill going before Congress next week.
However, there were signs that Colombia's biggest foreign donor, the US, would refuse to back the process.
Six senior American congressmen demanded tougher conditions be imposed on any disarmed paramilitaries.
In a letter the politicians said the guerrillas should be forced to confess to human rights abuses, disclose details of their drug smuggling rings and surrender criminal proceeds.
Accused of massacres
The US brands the paramilitary United Self-Defence Forces of Colombia, or AUC, a foreign terrorist organization.
They are accused of being deeply involved in cocaine smuggling, and of many civilian massacres.
Human rights groups have also said there are insufficient guarantees in Mr Uribe's bill that the paramilitaries will not return to arms.
But Mr Uribe rejects the US demands, saying the AUC will never sign up to them.
He told delegates from 24 countries in the city of Cartagena that his bill was fair and could be used as a framework for peace processes with other armed groups in Colombia.
It is estimated that demobilising the estimated 15,000 AUC fighters would cost the Colombian government more than $100m (£53m). Mr Uribe wants foreign donors to help fund the process.
The government is committed to retrain the guerrillas for civilian life.
More than 4,000 AUC members have already surrendered their weapons over the past few months.
Also on Thursday, the AUC said its previous chief, Salvatore Mancuso, had demobilised and was now in civilian life, and that Ramon Isaza Arango would take over as commander.