ETA has been fighting Spain for an independent Basque state since the 1950s.
The Basque separatist group ETA plans to fully lay down its weapons by April 8, a source close to disarmament talks said on Friday.
ETA, which has killed more than 800 people over several decades through bombings and assassinations, has enforced a unilateral ceasefire since 2011.
"The Basque government will do everything in its power to make sure this goes according to plan, even if not everything is in our hands," the Basque government's regional leader Inigo Urkullu said in a news conference on Friday.
He said the Basque government had been informed of a possible weapons handover.
TRT World spoke to Jaime Velazquez in Madrid with the latest on the story.
Txetx Etcheverry, an activist with the pro-Basque independence campaign group Bizi, told French newspaper Le Monde that ETA "will have completely handed over its weapons" by April 8.
Arnaldo Otegi, leader of far-left Basque pro-independence party EH Bildu, said the disarmament was an "exciting historical moment". Otegi was released from prison last year after a six-year sentence for belonging to an armed group.
"Let's hope that this time the weapons handover will be final," a smiling Otegi told a news conference.
ETA was formed in the late 1950s during the dictatorship of Francisco Franco with the aim of establishing an independent Basque state in northern Spain and southern France.
But the group has been severely weakened in recent years after hundreds of its members, including its leader, were arrested and police seized several of its weapons stashes.