Four security force members held by the Revolutionary Armed Forces of Colombia (FARC) rebels have been killed, Juan Carlos Pinzon, the Colombian defence minister said.
Pinzon told reporters that the four hostages, all held for more than 10 years, were killed execution-style on Saturday, three with shots to the head and one with a shot to the back.
He said that the bodies were found following combat in the country's south between troops and rebels.
Pinzon initially announced the deaths, and said hours later that a fifth rebel prisoner, Luis Alberto Erazo, a police sergeant who had been held for nearly 12 years, fled into the jungle and survived.
Colombian President Juan Manuel Santos called the killing of a soldier and three police officers "a crime against humanity" and dismissed any suggestions that Colombia's armed forces might be responsible.
"They were held hostage for between 12 and 13 years and wound up cruelly murdered," Santos said.
The FARC has a standing policy to kill prisoners to prevent their rescue, which makes rescue attempts dangerous. A senior defense ministry official told the Associated Press news agency, on condition of anonymity, that the government was not trying to rescue the now dead hostages.
But former Senator Luis Eladio Perez, who was freed by the FARC in February 2008 after six years of captivity, said that he believed the four died in a failed rescue.
The sister of one of the victims, 34-year-old police Major Elkin Hernandez, was angry with the government.
"The FARC are murderers for the manner in which they killed them, and the government is equally a murderer. They had the possibility to get them out of there, and they didn't," Margarita Hernandez told AP.
The FARC is known to hold about 20 security force members, some for more than 13 years. This would not be the first time the FARC has slain captives when under military pressure.
In June 2007, FARC fighters killed 11 regional legislators they had been holding for five years, apparently under the belief they were under attack by government forces.
Latin America's longest standing rebel army, the FARC took up arms in 1964 and has suffered a series of recent setbacks including the combat death earlier this month of its leader, Alfonso Cano.