Two people have been injured by flying shards of glass following a car bomb in central Bilbao.
The area was evacuated before the explosion in a busy shopping street.
A Spanish police spokesman said an anonymous caller phoned a warning to a regional newspaper and claimed the Basque separatist group ETA was responsible.
The blast occurred in the Gran Via street in Bilbao, in the northern Basque region.
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Police cordoned off the area before the blast, but were unable to identify which car contained the bomb, the spokesman said.
The explosion shattered the windows of a number of buildings in the area.
AP