By the turn of this century, tight co-operation between Spanish and French security forces had led to the arrest of numerous organisation's senior figures, leaving it severely weakened.
The group is due to formalise its dissolution at an official event later this week, drawing a line under an ultimately unsuccessful drive for an independent state in northern Spain and southern France that killed around 850 people.
"The Basque Country is now before a new opportunity to finally close the conflict and build a collective future", the ETA added. A spokesman for the Basque regional government told the AP that it received ETA's letter "a few days earlier". "Some are still bleeding, because the suffering is not in the past", read Eta's disbandment letter, which also said that the group "acknowledges the suffering caused as a result of its struggle".
Family members of ETA's victims say they are unconvinced the Basque militant group has had a change of heart despite announcing in a letter that it is disbanding.
The decision, ETA said in the letter, "doesn't overcome the conflict that the Basque Country maintains with Spain and with France".
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Almost half the deaths attributed to ETA have not been fully investigated, and many Basques feel there remain issues to be resolved before peace can be established.
"This is not the end of ETA that we wanted and, above all, is not the end of ETA we deserved", she said.
But Spanish Interior Minister Juan Ignacio Zoido said Wednesday that "they will not obtain a thing for making a declaration they call a dissolution".
Founded in the midst of Gen. Francisco Franco's regime, the group grabbed global headlines when it killed the dictator's anointed successor, Prime Minister Luis Carrero Blanco, in 1973. It remained active long after Franco's own death in 1975. But its move marks what is expected to be the last of several key steps towards the formal break-up of the once-armed separatist group, blamed for more than 800 deaths.
"The conflict did not start with ETA and it does not finish with the end of ETA's journey", it said.
Ms Ordonez's brother Gregorio, a leading regional figure in the conservative Popular Party, was killed by ETA in 1995.