BOGOTA - At least nine soldiers were killed in an attack by the National Liberation Army (ELN), the second largest guerrilla group in Colombia, the country's military said Wednesday.

The attack on soldiers with home-made explosives took place late Tuesday in northeastern Colombia near the border with Venezuela, the regional army command said in an online statement.

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

This was the second serious attack on Colombia's military since February when seven soldiers died in combat with the biggest rebel group, the Revolutionary Armed Forces of Colombia (FARC), with which Santos' government has been in peace talks for the past six months in Cuba.

The ELN has reportedly some 2,500 fighters.