Several Spanish newspapers say U.S. intelligence used Palma airport on the Mediterranean island of Mallorca from early 2004 to 2005.
El Pais reported that four planes had made at least 10 stops.
Defence Minister Jose Bono said there was no evidence, so he would not make accusations against Washington:
“We have no proof, so I am not prepared to put a friendly, allied government on the spot on the basis of supposition and rumour.”
The Washington Post reported this month that the CIA had a secret prison system in eastern Europe.
Kathalijne Maria Buitenweg is with the European Parliament’s Committee for Civil Liberties and U.S. relations.
“In case these alleged camps, if they really exist, yes, it is clear that the member states are co-responsible for whatever happens there.”
European Union Justice Commissioner Franco Frattini said on Monday there was no evidence any EU state had housed secret CIA centres, but any that had could face sanctions.