Spanish-born Inaki Imaz Munduate, 33, was wanted by Spain's judiciary for his "involvement in terrorist acts" and a European warrant was issued for his
arrest after he went on the run in 2007.
Munduate lived in Ireland "until a few months ago, hiding and with fake identity papers" provided by ETA, said the ministry.
"His presence in the country was in line with the terrorist group ETA's strategy to move parts of its organisation away so as to avoid the police in
A total of 18 people suspected of having links to ETA have been arrested this year, 12 of them in France.
According to the Spanish ministry, Munduate belonged to ETA's political wing, and was regularly in contact with both the organisation's management and
ETA members in the south of France to whom he gave "sporadic aid and technical advice".
Suspected of being a former member of ETA's commando unit Donosti, he is also accused of allowing the group to use his apartment in the northern
Spanish Basque city of San Sebastian to store weapons and munition, and of preparing reports detailing possible future attacks.
On June 29, police in London arrested another ETA suspect, Ignacio Lerin Sanchez, who Spain says is a "commando colleague" of Munduate.
ETA, listed by the European Union and the United States as a terrorist group, vowed in July to stick by a decision taken last October to abandon
violence in its fight for an independent homeland in northern Spain and southwestern France.
It refused however to disband.
Spain and France have refused to enter negotiations with ETA, demanding the group disarm and disband after four decades of bombings and shootings blamed
for more than 800 deaths.