Spanish Prime Minister Mariano Rajoy said yesterday there would be "no impunity" for ETA's crimes even though the Basque separatist group has committed to fully disbanding after more than four decades of violence.

"No matter what ETA does, there is no room for impunity for its crimes. ETA can announce its disappearance but its crimes do not disappear nor do the efforts to pursue and punish them," he said in a televised speech in the northern city of Logrono.

"We don't owe them anything and we have nothing to thank them for," Rajoy added.

His comments come as ETA is expected to formally announce its dissolution yesterday with a filmed statement, marking the definitive end to Western Europe's last armed insurgency after more than four decades of violence.

Created in 1959 at the height of Francisco Franco's dictatorship, ETA waged a relentless campaign of killings and kidnappings in its fight for an independent Basque homeland in northern Spain and southwest France, leaving at least 829 dead.

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. In a leaked letter published Wednesday by Spanish online newspaper El Diario, the group went a step further, announcing it was fully disbanding. "ETA has completely dissolved all of its structures and declared an end to its political initiative," it said.