The group is blamed for 829 deaths and thousands of woundings in a violent campaign to carve out an independent homeland in northern Spain and southwestern France.
Three of its militants, dressed in black with white hoods hiding their faces and wearing black berets, declared in a video a "definitive" end to the armed struggle.
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But they did not bow to earlier demands by the Spanish government and opposition for a total dissolution of the group, nor make a mention of an eventual disarmament.
"We are disappointed because this is not the last step," said Maria del Mar Blanco, a lawmaker with the conservative Popular Party in the Basque regional assembly.
Her brother was killed by the Basque separatist group.
"The terrorist group ETA must still definitively end," Blanco said in an interview with AFP.
"We will continue to work until we achieve its definitive dissolution without any type of negotiation, of exchange, and we must demand that they recognise the damage they have caused," she said.
ETA made no apology to the victims of its past actions in the announcement, offering instead its "deepest recognition and tribute" to comrades who had died in the "cruelty of the fight" or been imprisoned.
"They recognised their victims but they do not recognise the nearly 1,000 innocent victims that were assassinated by the imposition of a totalitarian political project," Blanco said.
ETA militants kidnapped her brother, Popular Party city councillor Miguel Angel Blanco, on July 12, 1997 and killed him 48 hours later, unleashing unprecedented anti-ETA protests nationwide.
Another association of family members of ETA victims, the Association of Victims of Terrorism, expressed scepticism.
"ETA says there is a definitive cessation but they do not say that there was a defeat so, for us, the victims, this statement is worthless," said the group's president, Angeles Pedraza.
"Of course we are happy that there is a cease to violence but there needs to be more," she told Spanish radio.
"They have to give up their arms, they have to dissolve and they have to ask their victims for forgiveness for the damage they have caused and of course they have to turn themselves over to justice.
"I don't believe in ETA, we don't believe assassins. This is just another statement, another little step, I don't believe them. It is the statement we expected but not the statement that we wanted."
