One of Colombia's most senior labour leaders leaders has accused the army of assassinating three union officials. However, the government maintains the men were armed leftist rebels.
The men were killed yesterday by troops sent to arrest them near the eastern town of Saravena - one of the most violent places in Colombia where Marxist rebels enjoy popular support.
Vice President Francisco Santos said the three belonged to the outlawed National Liberation Army, a 5,000-strong force with a strong presence in the oil-rich region near the border with Venezuela.
"They were union officials. But they were also mixed up in things which didn't have anything to do with their union work," Mr Santos told reporters.
Gen Luis Fabio Garcia said the men were carrying weapons and explosives when they were shot.
But the president of Colombia's largest labour organisation, the Central Workers' Union, said the officials died just one day after claiming the authorities were plotting to murder them.
"We consider this to be an assassination of union officials," Mr Carlos Rodriguez said. Amnesty International representatives, who yesterday met President Alvaro Uribe seeking guarantees for the security of human rights workers, called for an investigation.
Mr Uribe, a staunch US ally in the region, has stepped up his campaign against leftist rebels, who have been fighting for socialist revolution for 40 years in a conflict that has claimed tens of thousands of lives.
Groups such as Amnesty International have criticised the government's tactics, which have included mass arrests of suspects.
Mr Uribe says the number of killings of union officials has fallen during his government, which has overseen a steep fall in the number of violent deaths and kidnappings throughout the country. The Central Workers' Union says 90 were killed last year, and 29 so far this year.