A farmer was killed and four policemen were injured when a bomb exploded close to a passing patrol car on a highway near the southern Colombian town of Samaniego, close to the border with Ecuador.
The farmer was hit by the explosion while travelling along the highway. Authorities found and diffused several other explosives along the same road, the Nariño police department told Terra.
Those injured were rushed to hospital in Pasto, the capital of Nariño.
Authorities said they were unaware of the motive for the attack or who was responsibile.
Radio stations from Nariño noted that leftist guerrillas, right wing paramilitaries and drug traffickers are known to operate along the route between Samaniego and the nearby town of Tuquerres.