"Eta is not operational but it is alive," Interior Minister Jorge Fernández Diaz told reporters in Vitoria, the capital of Spain's Basque region.
"Any state of law will act against a terrorist organisation that is alive, in the sense that it has not disbanded. That is what we will do throughout our term in office."
Eta is blamed for the killing of 829 people in a four-decade campaign of bombings and shootings for an independent Basque homeland in northern Spain and southwest France.
Fernandez spoke after meeting with local officials to launch plans to build a museum in memory of ETA's victims.
His comments coincided with the third anniversary of Eta's declaration on October 20th, 2011 of a "definitive end to armed activity".
That was seen as more than a mere ceasefire, but a potential step towards the disbanding of western Europe's last major armed secessionist movement.
Three years later, Eta has made further token gestures of decommissioning arms and hinted it is ready to dismantle its logistical bases, but there is still no resolution in sight
The Spanish and French governments refuse to negotiate with Eta, insisting it formally disarm and disband without conditions.
"Today is a good day to renew our demand to those who killed and who supported the killers, that they acknowledge the harm they caused and apologize to the victims of terrorism and to society in general," Fernández said.
Only a few dozen active ETA members are thought to be still at large while hundreds are in French and Spanish prisons.
Meanwhile non-violent leftist Basque nationalist parties have gained increasing influence in regional elections.
A spokesman for the leftist Basque party Sortu, some of whose members were formerly in ETA's erstwhile political wing Batasuna, criticized the government's "intransigence".
The spokesman, Pernando Barrena, reckoned the Spanish government, already trying to contain a drive for independence in the northeastern Catalonia region, had little appetite for another secessionist debate.
"ETA has to take more steps forward and we are convinced they are going to do so and that they will carry through their disarmament to the end," he told AFP.