BILBAO, Spain - Tens of thousands of protesters marched through the streets of Bilbao in Spain's northern Basque Country on Saturday in support of jailed members of the Basque separatist group ETA, defying a court ban from Madrid.

A high court judge had vetoed the march, which was initially organized by prisoners' supporters to call for inmates to be moved to jails closer to their homes.

But two of the region's main political parties - the Basque pro-independence party Bildu and the more moderate nationalist PNV (Partido Nacionalista Vasco) - joined forces to restyle the rally as a march for "human rights, understanding and peace".

The treatment of ETA prisoners is an awkward one for the Madrid government, which would be certain to anger victims' associations if it made any concessions to the prisoners.

ETA - or Euskadi Ta Askatasuna, which means Basque Homeland and Freedom in Basque - is accused of killing more than 800 people over more than four decades, many with car bombs.

However, the group called a ceasefire in 2011, and speculation has grown that it might soon announce a full disarmament.

"This is a unique opportunity to show the world our desire for peace and the obstacles that the Spanish government is putting in the way," said Jose Mari Agirre, 55, at the march.

ETA prisoners' demands to see out their jail terms in the Basque Country could advance after they said last month they would recognize Spain's criminal justice system.

In a statement, the prisoners also acknowledged the pain caused by decades of violence.

The group has already been significantly weakened by hundreds of arrests in both Spain and France as well as a decline in political and social support in the Basque Country.

About 600 ETA members are in prison in Spain.