The military in Colombia says it is sending more troops to the eastern province of Arauca, a rebel stronghold, to deal with a recent wave of attacks.
The announcement comes hours after gunmen shot dead a local politician, Pedro Antonio Bohorquez, and his bodyguard in the city of Saravena.
Earlier on Tuesday, eight soldiers were also injured by a homemade explosive device in a separate incident.
The area, which borders Venezuela, is a stronghold of left-wing ELN rebels.
With an estimated 2,500 members, the ELN is Colombia’s second biggest rebel group.
It has been fighting the Colombian state for five decades.
On Tuesday, Colombia’s police chief, Rodolfo Palomino, offered a reward for information on the attackers.
“Reward of up to 50 million [Colombian pesos; $26,600, £15,800) to those who help us arrest the criminals who brought terror to Saravena,” Colonel Palomino tweeted after arriving in the city.