The government was at first quick to point the finger of suspicion at the Basque terrorist organization ETA, but Interior Minister Angel Acebes announced the arrest late Saturday of three Moroccans and two Indians in connection to the attacks. And early Sunday he disclosed that police had found a videotape in Arabic claiming that al-Qaida was responsible for the attacks.

Mr. Acebes said police followed a telephone tip and found the videotape in a waste paper basket near Madrid's principal mosque.

The tape showed a man dressed in Arab garb who spoke with a Moroccan accent. He said al-Qaida planned the Madrid attacks to take place exactly two and a half years after the September 11 attacks in New York and the Pentagon near Washington. He said the Madrid bombs were in retaliation for Spain's cooperation with what he called "the Bush criminals" and their actions in Afghanistan and Iraq. He threatened more such attacks.

Earlier Saturday the government announced the arrest of the Moroccans and Indian citizens, saying they had links to a mobile phone found in a backpack containing an unexploded bomb on one of the four trains attacked on Thursday.

The possible al-Qaida connection could have an adverse affect on the ruling Popular Party's chances of remaining in power.

Outgoing Prime Minister José María Aznar's staunch support of U.S. operations in Iraq has become an important campaign issue. His handpicked successor, Mariano Rajoy, has pledged to continue that policy despite the opposition in opinion polls of more than 80 percent of the Spanish people.

The head of the main opposition Socialist Worker's Party, José Luis Zapatero, has pledged to withdraw Spain's 1,300 soldiers from Iraq unless there is U.N. approval of the deployment.