Spanish Prime Minister Jose Maria Aznar has vowed to catch those responsible for the Madrid train bombings. "March 11, 2004, has taken its place in the history of infamy," the country's leader said in an emotional national address Thursday evening.

He said those who set off the 10 bombs in packed commuter trains during the height of rush hour would be hunted down and punished. He and other government ministries, as well as much of the country's news media, have pointed the finger at the Basque separatist group ETA, although evidence discovered in the last several hours could point towards a Islamic terrorist group associated with al Qaeda.

"We will defeat them (ETA)," Aznar said. "We will succeed in finishing off the terrorist band, with the strength of the rule of law and with the unity of all Spaniards."

ETA's handwork?

"Terrorist band" is a term the Spanish government regularly uses to refer to ETA, the armed group fighting for an independent Basque state in northern Spain. ETA has been involved in a string of bombings throughout the country since the late 1960s. More than 800 people have been killed in their attacks, which target both politicians and the civilian population.

Spain's Interior Ministry said tests showed the explosives used in Thursday's attacks were a kind of dynamite normally used by ETA. Aznar's office said the explosives contained a material called titadine, a kind of compressed dynamite found in a van intercepted last month as it headed for Madrid.

On Feb. 29, police intercepted the van packed with more than 500 kilos (1,100 pounds) of explosives traced back to the Basque separatists; two men were arrested on charges of terrorism. On Christmas eve, police thwarted an attempted bombing at Chamartin, another Madrid rail station, and arrested two suspected ETA members.

On Sunday, Spain goes to the polls in a general election. Debate over the handling of ETA had played a large part in the campaign, with the conservative ruling party pulling ahead in the polls. The party of Aznar had built its reputation on hard-line tactics against the separatist group.

Islamic terrorists at work?

Despite the likelihood of ETA's involvement, the government said it is keeping the lines of investigation open after evidence emerged that could possibly implicate Islamic extremists. In the town of Alcala de Henares east of Madrid, a stolen truck was found that contained detonators and an audio tape with verses from the Koran in Arabic, according to Interior Minister Angel Acebes.

Late Thursday evening, the London-based Arabic newspaper, al-Quds al-Arabi, issued a statement that it had allegedly received an e-mail a group calling itself Abu Hafs
al-Masri Brigades. In the letter, the Islamic terrorist organization, which has closely aligned itself with Al Qaeda claimed responsibility for the Madrid bombings.

The attack "was a part of the settling of old scores with crusader Spain, America's ally in its war against Islam," the statement said. "Where is America, O Aznar? Who is going to protect you," it asked.

The editor of al-Quds, Abdel Bari Atwan, said he believed the al Qaeda claim of responsibility was genuine. "In the past, the same organization sent us similar letters. They claimed responsibility for the attacks against Italian troops in Iraq and also for attacks in Istanbul against the British consulate," the editor told reporters.

German intelligence officials, however, are reported to be skepitcal of the group. The Brigade also claimed responsibility for a series of power outages and blackouts in North America last Fall. No U.S. law enforcement agency believes there was any foul play, much less a terrorist conspiracy, behind the blackouts, according to the Frankfurter Allgemeine Zeitung.

Minister Acebes said all possibilities were being investigated, although ETA remains the chief suspect.

ETA Denies Involvement

A political group close to ETA, the banned Basque separatist party Batasuna, denied that it was responsible for the attacks. In the past, ETA attacks have been preceded by warnings from the group. Officials received no such warning before Thursday's explosions.

Speaking on Radio Popular, Arnold Otegi blamed "Arab resistance" for the attacks, the worst in Spain's history. "Spain maintains occupation forces in Iraq and we should not forget that it had a responsibility for the war in Iraq," he said.

ETA, which stands for Basque Homeland and Freedom, was thought by many to be weakened and on its way out after the string of arrests and seizures of weapons. Only several dozen hard-core militants are believed to still be operating.

Most of ETA's attacks have been assassinations or small-scale attacks. If the Thursday bombings are its work, it represents a remarkable increase in scale, ruthlessness and coordination.

"This is a step ahead of previous attacks by ETA. It could be a splinter group, it could be hardliners trying to extract as many casualties as they could," Paul Wilkinson, a terrorism expert at the University of St. Andrews, told Reuters.

Worst terror attack in Spain's history.

Thursday's powerful explosions, which authorities say appear to have been set off by remote control, rocked several Madrid train stations during morning rush hour. The 10 simultaneous explosions which started at 7:30 am, local time, were designed to achieve maximum damage.

The bombings are being described as the worst in Europe since the 1988 bombing of Pan-Am flight 103, which was blown out of the sky over the town of Lockerbie, Scotland, and killed 270 people. They are the worst ever in Spanish history.

Prime Minister Jose Maria Aznar called for nationwide protests against the Basque separatist group ETA. "The government asks Spaniards to demonstrate tomorrow [Friday] in the streets of all of Spain... under the slogan 'with the victims, with constitution and for the defeat of terrorism'," Aznar said.

Across Europe and throughout the world, the attacks were met with shock and condemnation. "It is an outrageous unjustified attack on the Spanish people and Spanish democracy," European Parliament President Pat Cox said Thursday as the EU flags flew at half-mast. In Germany, Chancellor Gerhard Schröder said he was "deeply dismayed by this inhuman attack." He offered to send specialists from the country's Federal Criminal Office to Spain.

U.S. President George W. Bush spoke by telephone to the Spanish prime minister. "I appreciate so very much the Spanish government's fight against terror, their resolute stand against terrorist organizations like the ETA, and the United States stands with them," he told reporters.

Reflecting what many in his home country are thinking, he Spanish ambassador in Washington said, "This is our September 11."