A statement on Thursday attributed to al-Qaida and sent to the London-based daily al-Quds al-Arabi claimed responsibility for Thursday's serial bombings in Madrid that left 192 dead and over 1200 wounded.
The statement also claimed responsibility for the suicide attack on a Masonic lodge in Istanbul two days earlier and said a big attack on the United States was "imminent".
"We bring the good news to Muslims of the world that the expected 'Winds of Black Death' strike against America is now in its final stages...90% ready and God willing near," it said.
The statement also cautioined Muslims to stay away from "civilian and military institutions of crusader America and its allies."
The statement bearing the signature of "Abu Hafs al-Masri Brigades" linked to the al-Qaida network came amid claims by Spain's interior minister that a suspect van found near the scene of bombings contained seven detonators and an audio tape in Arabic.
The dead lay strewn all over the
scenes of bombings
The van had been stolen from the southern town of Alcala de Henares, which was the point of origin for the four trains targeted in the bomb attacks, Interior Minister Angel Acebes said.
The al-Qaida statement, yet to be authenticated, proclaimed "we have succeeded in infiltrating the heart of crusader Europe and struck one of the bases of the crusader alliance."
The statement dubbed the attacks as "Operation Death Trains".
Spanish authorities had initially blamed the bombings on Basque separatist group ETA.
But following the discovery of the stolen van, Acebes said "a new clue has been found and our duty and responsibility is to open a new line of investigation."
The minister insisted the "main lead remains the ETA, but we must be very cautious to investigate other leads."
He said the attackers had used 12 bags filled with between eight and 10kg of explosives.
"We are talking about more than 100kg of explosives composed of dynamite, which is what ETA usually uses," Acebes said.
The attack is the worst to hit Europe since the 1988 bombing of a US airliner over Lockerbie, Scotland that killed 270.
US intelligence agencies however said it was too early to say who was responsible for the attacks
A US official in Washington said, "There are characteristics of both ETA and al-Qaida-type of activity in this attack. So it's hard to know at this early stage who is responsible."
"At this point (we're) not ruling anything out, not ruling
"There are characteristics of both ETA and al-Qaida-type of activity in this attack. So it's hard to know at this early stage who is responsible"
anything in," the official said.
Earlier, the founder of ETA said the blasts did not bear the group's hallmarks.
Julen de Madariaga, who created ETA in the 1950s and was once its leader, said it would be unlike the group to attack busy, working-class areas. Thursday's blasts ripped through packed commuter trains at three stations in Madrid.
"It's not ETA's method of working," Madariaga told French television station LCI from the Basque city of San Sebastian.
Since leading ETA, Madariaga has turned his back on violence although he has been active in pushing for a political solution to the Basque question.
The director of the European police organisation Europol too cast doubts on Spanish government claims that ETA carried out the attacks.