MADRID (AFP) - A Spanish judge remanded in custody on Monday eight suspects accused of supporting prisoners from the armed Basque separatist group ETA.

High Court judge Eloy Velasco ordered the eight be held while they are investigated for the suspected crime of membership of a terrorist organisation.

In a written ruling, he said he remanded them in custody due to the risk that they could flee or destroy evidence.

Police arrested the eight on Wednesday in raids in northern Spain, the latest blow against ETA, western Europe's last major armed secessionist group.

ETA is blamed for the deaths of 829 people in a four-decade campaign of shootings and bombings for an independent Basque homeland in northern Spain and southwestern France.

Among those detained was Arantza Zulueta, a lawyer representing various ETA prisoners.

During their court appearance on Monday the eight refused to answer questions from the judge.

The arrests came two weeks after ETA prisoners softened key demands in an apparent bid to engage the Spanish and French authorities.

They said they were prepared to drop their insistence on a general amnesty and instead seek their release through legal channels.

The Spanish and French governments refuse to negotiate with ETA, branded a terrorist group by the European Union and the United States.

The treatment of imprisoned ETA convicts is one of the most delicate issues in a standoff between the authorities and the armed group, which has been weakened by the arrests of senior leaders in recent years.

Tens of thousands of protesters in Spain's Basque Country defied Madrid on Saturday by holding a mass demonstration marked by tensions over the prisoners.

Crowds filled the streets in the northern city of Bilbao in a march for "human rights, understanding and peace".

A judge had banned another demonstration planned to seek concessions for the prisoners, who are dispersed in jails across Spain and France to stop them coordinating.

Their families demand they be moved to jails closer to home.