Army general Omar Sepulveda said the migrants had been "co-opted" by Colombian guerrillas to launch the attack in El Tarra, a border town in the northeastern Norte de Santander department.

One soldier was killed by "an explosive device" and at least 16 others were wounded during the attack on Saturday.

"Approximately 95 percent" of the attackers were Venezuelans "institutionalized" by dissidents of the former Revolutionary Armed Forces of Colombia (FARC) rebel group, Sepulveda told W Radio.

The migrants tried to "overrun" the barracks using "improvised explosive devices, sling-shots, sticks and Molotov cocktails" he added.

Sepulveda blamed the attack on dissident Jhon Mechas, who refused to lay down arms and join the historic 2016 peace deal that turned the FARC into a communist political party following a half century of conflict with the state.

The region around El Tarra has the largest number of illegal coca leaf plantations in the world, according to the United Nations.

Coca is the main ingredient in cocaine and several groups of leftist guerrillas, right-wing paramilitaries and drug-traffickers are battling for territorial control to exploit the lucrative narcotics market.

Colombia's army said it was sending anti-riot troops to the region where local authorities declared a curfew until Tuesday morning.

Colombia has taken in 1.8 million Venezuelans fleeing poverty and economic crisis in their homeland.

President Ivan Duque accuses his Venezuelan counterpart Nicolas Maduro of harboring Colombian rebels in his country, granting them a safe haven from which to launch attacks.

Caracas denies the accusations.