BOGOTA (Reuters) - When the shooting started, police sergeant Luis Erazo scrambled into jungle canopy, the only escape from death as his Colombian guerrilla captors hurled grenades at him.
Four fellow hostages were shot dead by the FARC.
Erazo, held prisoner by the Revolutionary Armed Forces of Colombia for almost 12 years, was the only survivor when the FARC ordered the execution of captives as soldiers approached their hide-out during a weekend operation.
Three captors pursued Erazo, shooting and grazing him as he fled into the undergrowth.
"I heard the shots about 20, 30 meters from me and I thought, 'What's this, brother?'" Erazo told local radio.
"I felt the impact on my face and neck, the shots were at me, the only thing I could do was run."
In the southern jungles of Caqueta, the bodies of four members of Colombia's armed forces were found alongside their metal chains, three with bullets in their heads and a fourth shot in the back.
They had been held hostage by the drug-funded group for as long as 14 years, used as bargaining chips against the government.
The execution as troops closed in on the FARC hide-out is the most violent act by the rebels since special forces killed their leader, Alfonso Cano, earlier this month.
Saturday's mission began 45 days earlier after a tip that FARC captives were being held in the area. The four victims were shot as the military engaged rebels in a gun battle.
The government said Monday troops were attempting to locate the captives, not launch a rescue.
"They were tortured by more than a decade of captivity and then murdered," President Juan Manuel Santos said after the killings became public. "It's an atrocious crime."
Erazo eventually hid in a tree trunk, listening as the soldiers fought his captors. He crawled out when he heard chain-saws clearing trees for helicopters to land.
His companions had been pushed face down and shot in the back of the head, said a captured rebel. Another was shot twice in the back as he tried to escape.
The FARC, which still hold 11 military captives, had marched them through the jungle for weeks, Erazo said.
"Sometimes they were awful, at other times they were in a good mood and freed us from the chains. Sometimes we were chained from six at night until six in the morning," he told Colombia's Caracol radio station.
Saturday's killings may derail any behind-the-scenes attempts to bring the FARC to the negotiating table.
Santos said last week Colombia was nearing the final phase of nearly five decades of war and that he would be willing to talk peace if the FARC were serious and put down their weapons.
The rebels -- considered a terrorist group by the United States and Europe -- have refused.
Even as 10 years of military strikes have severely weakened the FARC -- attracting billions of dollars of investment to the oil and mining industries -- the fight against the Marxist group and other narco crime gangs strips as much as 1 percent from Colombia's economy each year.
The FARC, which calls itself "the people's army" defending peasant rights, has battled about a dozen administrations since first appearing in 1964, when its founder Manuel Marulanda and 48 rebels fought off thousands of troops in jungle hide-outs.
The group has faced its toughest defeats in recent years as U.S.-trained special forces use sophisticated technology and spy networks to track the leaders.
The FARC's string of defeats began in 2008 with a cross-border military raid into Ecuador that killed Raul Reyes, its second in command. Marulanda died of a heart attack weeks later and was replaced by Alfonso Cano.
Troops killed Cano earlier this month and he was replaced by Timoleon Jimenez, or "Timochenko," a hard-liner who has pledged to fight on.
Editing by Andrew Cawthorne and Vicki Allen