The tape along with the arrest of three Moroccan and two Indian suspects provided the strongest indication yet of an Islamic link to the attack on one of Washington's staunchest allies in Iraq. The Spanish government, however, said it could not confirm the tape's authenticity.

The announcement came just hours before polls were to open Yesterday in general elections weighed down by debate over the attack. Thousands of people rallied overnight against the governing Popular Party, saying it should be thrown out of power for drawing al-Qaeda's wrath.

A speaker on the videotape said the bombings were "a response to your collaboration with the criminals Bush and his allies" and threatened more attacks, Interior Minister Angel Acebes said in a hastily called news conference after midnight.