The Basque militant group ETA has announced that it has "completely dissolved all its structures," in a letter sent to Basque institutions and civil society groups.

In the letter, dated April 16 but only made public on Wednesday in Spanish online newspaper eldiario.es, ETA says it acknowledges its responsibility in failing to solve the Basque "political conflict."

ETA, whose initials stand for "Euskadi ta Askatasuna" — or "Basque Homeland and Freedom" — killed 853 people in its armed campaign to create an independent Basque state in northern Spain and southern France.

Responding to the announcement, Spanish Interior Minister Juan Ignacio Zoido vowed to keep investigating unresolved crimes attributed to ETA. He said police will "continue to pursue the terrorists, wherever they may be."

"ETA obtained nothing through its promise to stop killing, and it will obtain nothing by announcing what they call dissolution," he told reporters.