Colombian President Juan Manuel Santos said Saturday the killings by members of the Revolutionary Armed Forces of Colombia, commonly referred to as FARC, "could be the cruelest thing we have seen in a long time," Colombia Reports said.
"They had them as hostages, chained, and when they found themselves confronted with the security forces, showed no restraint in [assassinating] them in cold blood," Santos said.
The president said three of the men were shot in the head and the fourth was shot twice in the back.
The four -- three national police officers and an army soldier whose bodies were found Saturday-- were part of a group of 21 held by the guerrillas up to 14 years as political leverage, the Los Angeles Times reported. The executions took place in the jungles of Caqueta state in southern Colombia during a rescue attempt by the military, the newspaper said.
A fifth hostage fled to safety and one rebel was captured.
The FARC rebels have been battling the government forces for decades. Their longtime supreme leader, Alfonso Cano, was killed by the military this month. He has been succeeded by another rebel who goes by the alias Timochenko, the Times said.