A special peace tribunal said last week that six former FARC commanders may receive eight-year sentences "of non-carceral restriction of freedoms and rights."

Colombia's Special Jurisdiction of Peace (JEP) was set up to try the worst crimes committed during the conflict after a 2016 peace deal between the government and the once-powerful insurgent group.

"The victims feel disillusioned, so we have decided to withdraw. We will not find justice with the JEP," said the Foundation for the Defense of the Innocent, which represents some families of a group of 12 legislators who were kidnapped by FARC in April 2002.

The guerrilla group executed 11 of them in 2007 after years of captivity.

Some nine million people were killed, injured, kidnapped or displaced during the decades of conflict with the FARC.

The tribunal has yet to sentence the six commanders, who are accused of more than 21,000 kidnappings and other crimes committed between 1990 and 2016.

However, under the peace deal, it can offer alternatives to jail time to people who confess their crimes and make reparations to victims.

In June, the commanders admitted their "individual and collective responsibility" for the "abominable" crimes committed by their organization, which has since rebranded as a political party.

Franco-Colombian politician Ingrid Betancourt, who was held hostage by the group for six years before being rescued in 2008, said in a press release she would appeal what she dismissed as a "symbolic punishment."

Similarly, retired police general Luis Mendieta, who was held hostage by the rebels for 12 years, told local radio that the former guerrillas "did not respect the truth" and that the JEP has "no interest in administering justice."

The JEP has also charged 19 soldiers with war crimes and crimes against humanity for murdering 303 people, mostly civilians, who they pretended were rebels, to show they were making headway in the fight against the rebels.