In the 1980s, peace talks to end Colombia's long civil war instead triggered bloodshed. As the door opened for greater leftist power, thousands of former guerrillas, communist militants and trade unionists were gunned down by paramilitary death squads, sometimes in collaboration with state security forces, derailing the peace process and entrenching arguments for armed struggle.

Today, the government is pursuing peace again, and is promising leaders of the Revolutionary Armed Forces of Colombia that it will protect them and their fighters once they've laid down their weapons.

President Juan Manuel Santos is having a tough time persuading the rebels they'll be safe.

If current negotiations end the 50-year-old Marxist uprising, the job of protecting the peace likely will fall to the National Protection Unit, or UNP, a 3-year-old government agency that keeps watch over politicians, judges, high-profile activists and members of other historically threatened groups.

The unit's reputation, however, has been stained by the killing in August of a small-town journalist three weeks after the UNP withdrew its security detail.

Luis Carlos Cervantes was gunned down in Taraza, north of Medellin, as he went to pick up his son from school. Despite reports of death threats, the agency, which receives $250,000 a year in U.S. aid, had determined he was no longer at risk as a result of his past work denouncing local politicians for alleged ties to drug traffickers. Authorities have yet to make any arrests or determine a motive for the slaying.

The killing was followed days later by another setback: the exposure of a $300,000 kickback scheme that prompted authorities to arrest the unit's financial director and its No. 2 to flee the United States.

"If the UNP is having all these problems now, imagine what awaits when thousands of guerrillas come out of the jungle," said Carlos Guevara, coordinator of We Are Defenders, a Bogota-based group that stands up for human rights activists.

The promise of government-provided security for former combatants is part of a draft deal that has emerged from two years of peace talks underway in Cuba.

The guarantee is important not only given the fall-out of the 1980s peace effort, when as many as 3,000 leftists were killed, but because tensions are simmering again.

Since the start of the current talks, there's been a steady increase in reported attacks and threats against leftists, evidence of a dangerous rift between those who support the negotiations and those who fear that the president is ceding too much power to terrorists responsible for hundreds of atrocities.

In the first nine months of this year, We Are Defenders recorded 380 instances in which human rights activists were targeted by threats, arbitrary arrests or violence. That was up 44 percent from the same period of 2013, even while overall rates of homicide and kidnapping across Colombia have fallen to their lowest levels in a decade.

Carlos Lozano, a Communist politician who has been an intermediary to the FARC, says the government isn't doing enough to convince the rebels they will be safer on the streets than they are on the battlefield. Not only is there the threat of violence, but there is a lack of faith in a justice system that is both overburdened and compromised by powerful interests.

"There's no amount of armor plating or bodyguards that can generate the sort of confidence the FARC needs," Lozano said at the Community Party headquarters, where portraits honor slain members of the Patriotic Union, a party set up during the 1980s peace talks as a political arm of the guerrillas. "Santos wants a deal tomorrow, but he can't overlook the amount of mistrust that exists. Unfortunately peace takes time."

Lozano knows the importance of reliable protection firsthand. He is driven to work every day in an armor-plated SUV, escorted by as many as seven bodyguards paid for by the unit. In February, he was traveling with the Patriotic Union's presidential candidate in a turbulent northeastern state when gunmen on motorcycles opened fired on their eight-car convoy.

But he says his safety has been compromised in recent months, including the agency failing to provide an armored car to protect him while traveling outside Bogota and lacking enough money to pay the airfare of his bodyguards.

The UNP faces perennial budget shortfalls. In August, it threatened to withdraw protection from dozens of individuals before the government stepped in to fill a $15 million budget gap.

The unit currently provides protection to about 7,500 people. Politicians complain that taxpayers are burdened by its $200 million annual spending, which is equal to about $26,000 per protected individual, and many balk at the idea the agency would take on the added responsibility of protecting FARC rebels, currently estimated to number about 7,000.

Despite a steady decline in political violence over the last decade, the leader of the protection unit, economist Andres Villamizar, believes the left's obsession with security is well-justified.

Villamizar saw both of his parents targeted by Pablo Escobar for their fight against his once all-powerful Medellin drug cartel. His mother's kidnapping at the hands of the cocaine boss was dramatized in Gabriel Garcia Marquez's 1997 account "News of a Kidnapping."

"Ever since I was a little boy, I've been surrounded by bodyguards and seen what the lack of protection causes," he said. "In these cases, it's always better to sin on the side of excess."

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Joshua Goodman on Twitter: @APjoshgoodman

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Associated Press writer Libardo Cardona contributed to this report