Created in 1959 at the height of Francisco Franco's dictatorship, the ETA was blamed for hundreds of killings and kidnappings in its fight for an independent Basque homeland in northern Spain and southwest France.
Basque separatist group ETA formally declared its dissolution on Thursday, marking the definitive end to western Europe's last armed insurgency after more than four decades of violence.
In what it said was its final statement, the group announced it had "completely dismantled all its structures" and "put an end to all its political activity."
"ETA wishes to end a cycle of the conflict between the Basque Country and the Spanish and French states," it said in the statement dated May 3, and released to international media.
An audio recording of the statement being read in several languages by veteran, high-level ETA member Jose Antonio Urrutikoetxea – better known as Josu Ternera – and jailed ETA militant Marixol Iparraguirre was published on the website of Gara, a Basque regional newspaper which has traditionally been the group's mouthpiece.
ETA was blamed for the deaths of at least 829 people during its armed campaign.
TRT World's Ben Said has more.
The group's highest-profile killing was that of Franco's prime minister and heir apparent, Luis Carrero Blanco, in a Madrid car bombing in 1973.
Weakened in recent years by the arrest of its leaders, ETA announced a permanent ceasefire in 2011 and began formally surrendering its arms last year.
ETA had already announced that it would be fully disbanding in a letter leaked on Wednesday and addressed to various groups and figures involved in recent peace efforts.
International mediators will hold a peace conference in southwest France on Friday. Irish former Sinn Fein party leader Gerry Adams and representatives of several Spanish political parties are expected to attend.
Spain's conservative Prime Minister Mariano Rajoy earlier on Thursday dismissed the planned announcement of ETA's disbanding as "noise and propaganda" and vowed there would be "no impunity" for the group's crimes.
"ETA can announce its disappearance, but its crimes do not disappear, nor do the efforts to pursue and punish them," he said in the northern city of Logrono.
"We don't owe them anything, and we have nothing to thank them for."
While an overwhelming majority of Basques welcome the end of violence, many still want independence.
The separatist coalition EH Bildu, the second largest grouping in the regional parliament, won 21 percent of the votes in the 2016 regional elections.
The party has long called for the roughly 300 ETA prisoners held across Spain and France to be transferred to jails closer to the Basque region and their families.
The regional leader of Spain's Basque Country, Inigo Urkullu of the nationalist PNV party, said he hoped Madrid would soon bring ETA prisoners closer to the Basque region.
"ETA never should have existed. It puts an end to a dark chapter of 60 years," he added in an interview published earlier on Thursday in Spanish newspaper El Pais.
Victims reject "farce" announcement
ETA's announcement was rejected by victims' groups, who argue the separatist group should first and foremost condemn its history of violence and shed light on more than 350 unsolved crimes.
A partial apology by the separatist group last month in which it acknowledged the harm done and apologised to some of its victims – but not to those it considered legitimate targets such as police – has done little to stem the criticism.
"The victims are watching with pain and stupor how ETA is being allowed to direct this farce," the Victims of Terrorism Association (AVT) said in a statement.
Apart from ETA victims, there were also at least 62 separatists killed by far-right groups and death squads backed by members of Spain's security forces, in what has become known as a "dirty war" campaign.
And according to a December report commissioned by the Basque regional government, more than 4,100 complaints of police torture were made between 1960 and 2014.
Those victims are also demanding they be acknowledged.
"If you don't recognise part of the suffering, it's very difficult to create conditions for ... reconciliation," said Ane Muguruza, 28.
Her father Josu, a lawmaker for Herri Batasuna, ETA's political wing, was murdered in 1989 by far-right militants she believes were state-backed.
"It's very difficult when there are open wounds," she said.