Three warlords from one of Colombia's most notorious paramilitary groups have been allowed to speak in Congress.
Mancuso (left) told Congress his men were heroes
The right-wing AUC (United Self-Defence Forces of Colombia) is accused of mass killings and drug trafficking.
Its commander, Salvatore Mancuso, told Congress in the capital Bogota that his group was willing to work towards a permanent ceasefire.
But critics said allowing him such a high-profile platform undermined the credibility of the peace process.
Separately, the US Democratic Party's presidential candidate, John Kerry, has urged the Colombian President, Alvaro Uribe, to tackle human rights abuses in his country.
In a letter, Mr Kerry, his running mate, John Edwards and 21 US senators expressed concern about reports of human rights abuses allegedly committed by paramilitaries.
They called on Mr Uribe to follow United Nations recommendations for resolving the issue.
Mr Mancuso and his colleagues Ramon Isaza and Ivan Roberto Duque swapped their usual combat clothes for suits, as they were picked up from the jungle and flown by the air force to Bogota.
Although Mr Mancuso is wanted by the US for cocaine trafficking, they were guaranteed immunity from arrest.
In his speech he said: "In Colombia today nothing is more urgent and pressing
than opening paths of peace and reconciliation."
The AUC formally began peace talks with the government earlier this month.
Mr Uribe is keen to disarm paramilitary groups as part of his attempts to bring to an end Latin America's longest-running civil war.
But there were protests outside Congress at the paramilitaries' presence.
"The peace process should only take place at the negotiating table, where the paramilitaries surrender themselves to justice in return for certain benefits," Carlos Gaviria, a leading opposition senator, told AP.
Demonstrators protested at the AUC's presence
The BBC's Colombia correspondent, Jeremy McDermott, says the AUC is the country's most brutal warring faction, having carried out massacres and assassinations to "cleanse" large tracts of the country of Marxist rebels.
Thought to be between 13,000 and 20,000-strong, it has long been on European and US lists of terrorist organisations.
The US and others believe the AUC is a drugs cartel moving some 40% of the 800 tons of cocaine that leaves Colombia every year.
Mr Mancuso denies it is linked to drugs trafficking, saying his forces just levy a tax on coca growers in their region.
The AUC says it was forced to take up arms because the state failed to defend the people against guerrilla kidnapping and extortion.
In his speech Mr Mancuso refused to apologise for the deaths caused by his group and referred to his fighters as "heroes".