Forensic scientists in Colombia are investigating the death by poisoning of a soldier in eastern Arauca province.
The soldier died and at least six others fell ill after eating pork they had bought from a local person.
The military suspects the meat was laced with rat poison and that the person who sold it to the soldiers was a member of the ELN rebel group.
The group has an estimated 2,500 members and has been fighting the Colombian state for five decades.
In June, the ELN - Colombia's second largest rebel group - said it would enter into formal peace talks with the government.
But it has continued to carry out attacks in its stronghold on the Venezuelan border.
The military has also stepped up its operations against the guerrilla group in Arauca.
In a statement the army said its men had been set up by "a man disguised as a local farmer who turned out to be an ELN rebel".