The arrest provides the latest test for whether Belfast offers a haven for Basques wanted for questioning in Madrid. Two other recent extradition cases ended in failure — one because the Belfast judge rejected Spain's case, the other because the suspect jumped bail.
The Police Service of Northern Ireland said its officers arrested a 40-year-old man Thursday in central Belfast and took him to the force's interrogation center in Antrim west of Belfast.
Spain's Interior Ministry identified the suspect as Fermin Vila Michelena and said he faced three Spanish arrest warrants over a string of ETA attacks. The ministry statement accused Michelena of membership in an ETA terror cell that committed four car-bomb attacks in Spain in 2001.
ETA has killed more than 825 people, mostly in Spain, since the late 1960s in hopes of carving out an independent Basque state in northeast Spain and southwest France.
ETA leaders long have maintained close links with the outlawed Irish Republican Army and its sister Sinn Fein party, but they failed to emulate the Irish movement's 1990s transition from bloodshed to politics in the British territory of Northern Ireland.
Whereas Sinn Fein today helps lead Northern Ireland's government following IRA disarmament in 2005, an ETA cease-fire in 2006 soon crumbled and ETA's allied Batasuna party remains banned in Spain.
But ETA members and supporters continue to flock to Catholic west Belfast, where they can find a friendly home among members past and present of various factions of the IRA.
In November, Belfast judge Tom Burgess rejected a Spanish extradition warrant for a 33-year-old Basque man accused of past membership in an ETA-linked youth group.
In March, Burgess ordered the extradition of a senior ETA veteran, 55-year-old Jose de Juana Chaos, but he appealed the judgment and skipped bail the following month. Spain has accused de Juana Chaos of "praising terrorism" in a letter following his 2008 release from prison.