Spanish authorities are today examining a video tape featuring a purported spokesman for al Qaeda who claims responsibility for the Madrid bomb attacks.
The claim of responsibility for the atrocity which left 200 dead and 1,500 injured emerged late last night.
Hours earlier, Interior Minister Angel Acebes announced that five people, including some with possible links to Moroccan militants, had been arrested in the first breakthrough in the investigation of Thursday's near-simultaneous attacks on four commuter trains.
Mr Acebes said today police had not been able to identify the spokesman referred to on the tape. "We have not been able to identify the person...in whose name the attacks were claimed. Neither the French, British nor Portuguese services have any knowledge of this person."
If al Qaeda involvement is confirmed, it would be the first time the Islamic militant group has struck in the West since the attacks on New York and Washington on September 11th, 2001.
Under outgoing Prime Minister Jose Maria Aznar, Spain has been a close ally of the United States, firmly supporting US policy on Iraq and sending 1,300 troops there after the war.
The claim of responsibility came in the videotape recovered by Spanish police from a waste paper bin on the outskirts of Madrid after a television station received a call saying the tape was there.
On the tape, a man speaking in Moroccan-accented Arabic says al Qaeda launched the attacks in retaliation for Spanish co-operation with the United States and its allies.
"If you don't stop your injustices, more blood will flow and these attacks are very little compared with what may happen with what you call terrorism," the man said, according to a Spanish transcript provided by the Interior Ministry.
The statement referred specifically to Iraq and Afghanistan, both countries where Spain has sent troops to keep the peace.
The man noted that the Madrid blasts came exactly two-and-a-half years after the September 11th attacks.
"He makes the statement in the name of someone claiming to be the military spokesman of al Qaeda in Europe, Abu Dujan al Afgani," Mr Acebes told a news conference.
Mr Acebes said the name was not known to intelligence services and that investigators were examining the tape's authenticity.
The Interior Ministry did not release the video itself.
Mr Acebes said the man speaking on it wore Arab dress and had his face uncovered. At an earlier news conference Mr Acebes said investigators had found no evidence of suicide bombers.
The video was released after thousands of anti-government protesters took to the streets across Spain on last night demanding to know "the truth" behind the rail bombs, denouncing the ruling Popular Party (PP), and shouting slogans like "Don't Manipulate Our Dead!"
The latest developments call into question the Spanish government's initial insistence that armed Basque separatist group ETA was the prime suspect behind the bombs. Mr Acebes said both lines of investigation remained open.