MADRID, March 11 (Xinhuanet) -- Spain witnessed a bloody day Thursday when a series of powerful explosions ripped through three busy trains in the capital of Madrid, killing at least 190 commuters and wounding more than 1420 others.

    The blasts were the worst terror attacks in Europe since the 1988 bombing of a Pan Am airliner over Lockerbie, which killed 270 people.

    No one has yet claimed responsibility for the deadly attacks.

    Spanish authorities blamed the blasts on the Basque separatist group ETA -- Basque Homeland and Freedom, but a London-based Arabic newspaper said it had received a claim of responsibility in the name of al Qaida.

    "The Brigade of Abu Hafs al-Masri in the name of al Qaida had penetrated one of the pillars of the crusade alliance, Spain," said an e-mail received by the Al-Quds al-Arabi newspaper.

    "This is part of settling old accounts with Spain, the crusader,and America's ally in its war against Islam," it added.

    The alleged claim, which could not be independently verified, came after reports said Spanish investigators found an Arabic language tape with Koranic versus in a van carrying bomb detonators near Madrid.

    The United States on Thursday denied suggestion that al Qaida was behind the deadly bombings in Spain and believed ETA was responsible.

    "The Spanish government has made clear that they believe, basedon the evidence they've collected and the patterns they've detected, that ETA is responsible for this. That's a Basque terrorist organization," State Department spokesman Richard Boucher said at a news briefing.

    Spanish government officials echoed the US judgment, saying ETAwas more likely behind the terror attacks.

    "It is still not proven that it is an authentic claim of responsibility," said an official from Spanish Prime Minister JoseMaria Aznar's office, who declined to be named. "We think there are more possibilities that it is ETA than any other organization."

    "The conclusion of this morning that pointed to ETA right now is still the main line of investigation. I have given the securityforces instructions not to rule out anything," Interior Minister Angel Acebes told reporters.

    ETA, which is listed as a terrorist group by the United States and the European Union, has killed more that 1000 people since 1968 in a campaign for an independent Basque state in northern Spain and southwestern France.

    If it was confirmed as ETA, the attacks could signal a change of strategy for the group that has mainly targeted policemen and politicians in its decades-long armed fight.

    The attackers evidently intended to intimidate voters as the blasts came three days before the general elections scheduled for Sunday, said analysts.

    The banned group ceased most of its active operations after about 190 members were arrested last year during a police crackdown. But it was accused of trying to plant bombs on a passenger train bound for a Madrid station earlier this year.

    Police also intercepted a van packed with explosives outside Madrid and apprehended two alleged ETA members on Feb. 29.

    Mariano Najoy, candidate from the ruling conservative Popular Party (PP), was favored in the opinion polls to beat his rival Jose Luis Rodriguez Zapatero from the opposition Socialist party in the upcoming elections.

    Prime Minister Aznar sent his condolences to victims of the blasts Thursday and vowed to hunt down the perpetrators.

    "This is a mass murder," Aznar said after an emergency cabinet meeting.

    "We will not back down in the face of terrorist killings. The criminals will be tried and convicted," he added.

    The purported ETA attacks were also aimed at forcing the government into negotiations with the Basque separatist group.

    Aznar's government has insisted on crushing ETA with police measures. "No negotiation is possible or desirable with these assassins who so many times have sown death all around Spain," he said Thursday.

    ETA announced a unilateral cease-fire in the northeastern region of Catalonia on Feb. 19, which was rejected by the Spanish government as "traps."

    Public anger at the mass killings of civilians will benefit Aznar's PP at Sunday's polls because of its hard-line policy against ETA, analysts said.

    The government called for nationwide anti-ETA rallies on Friday.Thousands took to the streets in Madrid and Victoria, capital of Basque region, in spontaneous demonstrations.

    The carnage also drew condemnation from governments and international organizations from around the world Thursday, including the United Nations, the United States, Russia, China, the European Union and the Arab League. Enditem