By Luis Jaime Acosta
BOGOTA (Reuters) - Colombia's Marxist-led FARC guerrillas killed five soldiers in an ambush on Friday just hours before the rebels were to begin an indefinite ceasefire, the army said.
Three police officers were also killed in an attack by the Southern American country's smaller ELN guerrilla group.
The Revolutionary Armed Forces of Colombia (FARC) ambush, in which seven soldiers were wounded, occurred in the southwestern province of Cauca as the army patrolled a highway damaged in a bomb attack a short while earlier.
The soldiers were killed by explosions and machine-gun fire, the army said.
The policemen died in a separate attack in northeast Norte de Santander province, which police blamed on the National Liberation Army, or ELN.
The FARC unexpectedly announced on Wednesday that it would cease hostilities for an unlimited time from Saturday. The government has rejected a rebel demand that an independent international organization monitor the ceasefire, however.
The rebel group has not commented on the plan since, casting doubt over whether it will hold to its promise of a truce.
The government of President Juan Manuel Santos has engaged in slow-moving peace talks with the FARC since late 2012 in an effort to end a five-decade-old conflict that has taken about 220,000 lives and left millions uprooted from their homes.
(Writing by Peter Murphy; Editing by Tom Brown)