Spanish police arrested three Algerians and a Spaniard on suspicion of recruiting for al-Qaeda.
Police arrested another Algerian earlier, but he was later freed when it was discovered he had no links to the alleged crimes, an Interior Ministry spokesman said.
The arrests in Madrid, Barcelona, Bilbao and the Cantabria region were part of Judge Baltasar Garzon's investigation into suspected al-Qaeda cells operating in Spain, a court official said.
"It was an infrastructure and support cell suspected of Islamic terrorism that could have recruited people to send to al Qaeda training camps," an Interior Ministry spokeswoman said.
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The arrests were not part of the probe into the March 11th train bombings in Madrid, officials said.