Belgian authorities have arrested Mr Youssef Belhadj, a Moroccan wanted by Spain in connection with the March 11th Madrid train bombing, the Belgian state prosecutor's office was quoted as saying.
Mr Belhadj (28) is suspected of having appeared on a videotape claiming responsibility for the Madrid attacks and describing himself as the spokesman of al-Qaeda in Europe.
"This suspect was apprehended this evening in Brussels. He is under a European arrest warrant issued by the Spanish authorities in connection with the Madrid bombing," national news agency Belga quoted Lieve Pellens of the Belgian prosecutor's office as saying.
Mr Belhadj, who Spain wants extradited, was born in Morocco but currently lives in Belgium, where he was arrested last March but then released.
More than 100 suspected Islamic militants have been arrested in Spain since the March attacks, although many have been released for lack of evidence.