Thousands demonstrated here on Saturday against a decision by the Spanish authorities to ban a Basque separatist coalition from running candidates in European Parliament elections next month.

Between 10,000 and 15,000 people marched through the city centre behind an enormous Basque flag to protest a supreme court decision to stop Herritarren Zerrenda (HZ), from taking part in the poll on June 13.

Madrid has accused the grouping of being a continuation of the pro-independence Basque group, Batasuna, whose activities have been banned because of its links to the armed separatist group ETA.

ETA is held responsible for the deaths of over 800 people in a three-decade struggle to establish an independent homeland in Spain's northern Basque region.

Protesters taking part in the peaceful march shouted "independence" and "democracy" and held banners that read "Basque Country Free". They also handed out leaflets with the banned list of candidates of Herritarren Zerrenda, which translates as "Citizen's List".

Batasuna spokesman Arnaldo Otegi attacked Spain's socialist government, telling the crowd in a speech at the end of the march that it had done nothing more than give the green light to the policies of the previous conservative administration.

Meanwhile a simultaneous protest by about 2000 Basque supporters was held in the southern French city of Bayonne, just across the border from the Spanish Basque country.

Demonstrators there were protesting a European arrest warrant issued by a Spanish judge against three alleged French Basque militants.

Yves Machicotte, Hartitza Galarraga and Amaia Rekarte, aged between 22 and 25, are all members of the Basque youth movement Segi, which is banned in Spain.

They are wanted in Spain on charges of belonging to a terrorist organisation. A decision on their fate is due to made by a French appeals court on Tuesday.

Minor clashes between security forces and demonstrators broke out at the demonstration later on Saturday after youths began pelting the police with beer cans. The police responded by firing tear gas. No injuries were reported.