BOGOTA (Reuters) - The biggest hurdle to signing peace with Colombia's FARC rebels and ending a half century of war is getting the Marxist group to agree to face punishment for human rights abuses, President Juan Manuel Santos told Reuters.
Government negotiators have spent more than two years in peace talks with the Revolutionary Armed Forces of Colombia (FARC), trying to end a conflict that has killed more than 220,000.
Although the talks in Cuba have advanced further than previous efforts, FARC commanders have said they will not serve a single day in jail.
"The bottom line is transitional justice. The guerrillas have said they won't go to jail, they don't want to submit to transitional justice, but amnesties of yesteryear are no longer possible," Santos, 63, said in an interview late on Tuesday.
"That's the crux of the problem."
Measures of so-called transitional justice in countries emerging from war include setting up truth commissions and reparations for the victims of human rights atrocities.
Colombia's justice system allows for reduced punishments such as house arrest and community service. Santos has refused to say which options are under discussion at the secret peace talks but he said he understands the 8,000-strong FARC's reluctance to swap the rebel ranks for a prison cell.
"Jail doesn't necessarily mean behind bars ... Jail can be defined in many ways," he said, although he insisted there has to be some punishment. "We want the maximum justice that allows us to achieve peace."
The talks have focused on five areas - the FARC's future participation in politics, an end to the illegal drugs trade, agricultural reform, reparations for victims and rebel demobilization.
A former journalist whose family founded Colombia's biggest newspaper, the center-right Santos said FARC leaders must confess to their crimes, repay victims and vow to permanently give up weapons.
He has staked his reputation on getting a peace deal and his re-election last year became a referendum on the talks, splitting the nation between supporters and those who charge that he has offered the FARC too many concessions.
Some fear the peace deal may violate international treaties by effectively pardoning war crimes and that victims will turn to international courts for redress.
The FARC took up arms in 1964 and at the height of the insurgency it controlled huge areas of land, but it has been weakened over the last decade by a U.S.-backed military offensive.
Colombia already has a transitional justice law, passed in 2005 to demobilize 30,000 right-wing paramilitary fighters. They received short jail terms in return for confessions, returning stolen land and compensating victims, but human rights groups say many of the promises were not met.
Additional reporting by Julia Symmes Cobb; Editing by Kieran Murray