A Spanish judge on Friday banned a mass demonstration planned to support jailed members of armed Basque separatist movement ETA, as the group pushed for concessions from authorities.

The treatment of ETA's jailed members is one of the most sensitive issues in a standoff between the Spanish and French governments on one side and western Europe's last major armed secessionist movement on the other.

Tens of thousands of people took to the streets Saturday in northern Spain to protest a crackdown on an association that aids jailed members of armed Basque separatist group ETA.

The protest in Bilbao came after police arrested 18 leaders of Herrira, a support group founded to help ETA prisoners and their families, in a series of raids on September 30.