Colombia's right-wing paramilitaries are likely to remain as strong as ever despite a new law regulating their de-mobilisation, activists have warned.
Some 9,000 fighters are said to have given up their arms
Amnesty International says the Justice and Peace law will in effect provide an amnesty and let them act with impunity.
The law has been very controversial but on Tuesday it received the backing of the Organization of American States.
All sides in the conflict - left-wing rebels, paramilitaries and state forces - have been accused of atrocities.
Tens of thousands of civilians are known to have been killed in the 40-year conflict.
Amnesty International says the situation in the Colombian city of Medellin - where a paramilitary unit handed in its arms two years ago - highlights shortcomings in the new law.
The rights group says the disarmament of the Cacique Nutibara Bloc was a dangerous farce: the fighters simply passed themselves as security guards or police informants, and still controlled many districts.
Medellin Mayor Sergio Fajardo called the report irresponsible and damaging.
Amnesty International says that across the country more than 2,300 killings and "disappearances" have been attributed to the paramilitaries since their umbrella organisation, the AUC, declared a ceasefire in December 2002.
The Justice and Peace law recently passed by congress limits the time for investigations into any atrocities, as well as the jail sentences that can be served for them.
Amnesty says this will merely "recycle" paramilitary fighters - for example, allowing them to work for the security forces or civilian informer networks - and allow them to act with more impunity.
It also denies the victims' rights to truth, justice and reparation, says the London-based group says, which is calling for the law to be repealed.
President Alvaro Uribe has defended the law saying it introduces justice and reparation to victims.
"It is not a law - like others already applied in Colombia or other countries worldwide - of pardon and oblivion," he said recently.
The Colombian government says that 9,000 of the 19,000 fighters the AUC says it has have disarmed under the peace process.
It expects to conclude the de-mobilisation process - which is being monitored by the OAS - this year.
The government has in the past held peace talks with the two main left-wing guerrilla groups, the Farc and the ELN, but both these processes have been broken off.