At least seven Colombian soldiers were killed and 30 wounded Thursday when a guerrilla group attacked an Army base with drones and explosives, the military said.

The attack, which happened at Military Base 27 in the northern department of Cesar, was attributed to the National Liberation Army (ELN), a Colombian group designated a terrorist organization by the US State Department and the European Union.

“In this terrorist act, the criminals used drones equipped with improvised explosive devices and carried out the indiscriminate launching of unconventional explosive devices,” the Army said in a statement.

According to reports, the soldiers were resting in hammocks after a day of training when they were attacked.

The wounded soldiers were evacuated to medical centers in the region, while Army units carried out operations to secure the area, according to the military.

The deceased soldiers were identified as Jaime Alejandro Cárdenas Ramírez, Mateo Pino Pulgarín, Juan David Pérez Vides, Kevin Andrés Méndez Torres, Jhon Fredy Moreno Sierra, Brandon Daniel Valderrama Martínez and Jorge Mario Orozco Díaz.

Defense Minister Pedro Sánchez Suárez condemned the attack and said the threat posed by the ELN must be dismantled. “Failure to do so puts the population at serious risk,” he said.

The minister added that although the armed forces have prevented “around 95% of drone attacks, this threat has grown exponentially and at a very rapid pace, which seriously jeopardizes national security.”

The attack happened after the ELN declared a nationwide “armed strike” in protest over what it called “threats of imperialist intervention” by the United States. The strike prevented civilians from traveling and paralyzed daily activity in areas where the ELN has influence.

The armed strike was accompanied by violent actions against infrastructure and public forces.

Authorities said they will release more information as the investigation progresses. (CNN)