Nine soldiers were killed and six wounded in an attack the government blamed Wednesday on the ELN, Colombia's second largest leftist guerrilla group.

The soldiers were attacked with home-made explosives in north-eastern Colombia near the border with Venezuela, officials said.

President Juan Manuel Santos broke the news in a message on Twitter. "Six heroes of our army (died) in an ELN attack in Norte de Santander. Our hearts are with their families."

The regional army command later issued a statement raising the death toll to nine.

The soldiers were ambushed late Tuesday "with home-made explosives" in the municipality of Chitaga, in the department of Norte de Santander, the statement read.

On April 14, three soldiers were killed in the nearby department of Arauca in an attack also blamed on National Liberation Army fighters.

The ELN, believed to have some 2,500 fighters, has been active for 48 years, although it has often been overshadowed by the much larger Revolutionary Armed Forces of Colombia (FARC).

The ELN was inspired mainly by the Cuban revolution and the ideas of Argentine revolutionary Ernesto "Che" Guevara. But it was also influenced by the Catholic Liberation Theology movement and guerrilla-priests like Camilo Torres and the Spaniard Manuel Perez.