Tens of thousands of protesters filled the streets of downtown Bilbao late Saturday to call for an amnesty that would allow ETA prisoners to serve out the remainder of their sentences in the Basque region, rather than in jails further afield.
The march in the northern Spanish city was the first trial of strength between separatists and the conservative governing Popular Party since the Nov. 20 general election.
Marchers unfurled banners saying "The solution, Basque prisoners to the Basque region," and marched mostly in silence to avoid confrontations with riot police under orders to dissolve the gathering if pro-ETA chanting broke out.
Rodolfo Ares, the region's Interior Ministry representative, had warned protesters to make their demands reasonable, saying calls for the early release of prisoners jailed for terrorist offenses was unrealistic.
"Prison sentences are there to be served," he said.
Spain has for 22 years dispersed ETA prisoners under an amendment to the country's 1975 anti-terrorism law. There are an estimated 700 ETA prisoners held in jails dotted around Spain and France, of which only around two dozen are believed to be serving sentences in the Basque region.
One of the purposes of the law was to stop convicted terrorists from communicating easily among themselves to plan subversive strategies.
Although ETA pledged in Oct. to stop using weapons in its bid for Basque independence, it stopped short of saying it would disarm and allow inspections of decommissioned weapons, as happened with the IRA in Northern Ireland.
ETA has killed 829 people since the late 1960s in bombings and shootings to force the creation of a Basque homeland in northern Spain and southwest France.
Although ETA _ classified as a terrorist organization by Spain, the United States and the European Union _ has declared two previous "permanent" cease-fires, many observers think this time they mean it. Waves of arrests in recent years have repeatedly weakened its structure and diminished its ability to perform acts of terror or collect funds.
Associated Press writer Harold Heckle in Madrid contributed to this report.