He said police investigations would "soon yield fruit." Spanish Foreign Minister Ana Palacio said today that available evidence continues to point to the armed Basque separatist organization ETA as being responsible for the blasts. She said she does not rule out the possibility that some other groups, including Islamic radicals, might have directed the attacks.
Spain's interior minister, Angel Acebes, yesterday blamed ETA but said he has instructed security forces to consider other possibilities also. His comments followed the discovery of detonators and a tape with Koranic verses in Arabic in a stolen van east of the Spanish capital.
Arnaldo Otegi, leader of the banned Batusana party -- the suspected political wing of ETA -- said yesterday it is inconceivable that ETA was involved in the bombings. "Neither the objectives nor the modus operandi can confirm that ETA is behind what happened today in Madrid," he said. "We would like to make that absolutely clear. Secondly, we would like to express our solidarity with all the relatives of the victims and to the whole population of Madrid."
He blamed what he called "Arab resistance" to Spain's role in the Iraq war.
Batasuna, which denies any organized links with ETA, has been banned by the Spanish government for refusing to condemn the radical Basque separatist group. Koldo Gorostiaga, Batasuna's representative in the European Parliament, yesterday condemned what he described as the Madrid "massacre" and said it had "no justification."
Terrorism experts say the 10 synchronized explosions in Madrid are unlike anything ETA has done in its 36 years of battling for an independent Basque state. Instead, ETA is known for planting small bombs that strike selected targets. It usually phones in warnings to police ahead of time or takes responsibility for blasts immediately afterward.
But authorities point to evidence that ETA's methods could be changing. Last month, Spanish police said they intercepted a van carrying more than 500 kilograms of explosives headed to Madrid. And in December, police said they foiled a suspected ETA bomb attack on a Madrid train station. They said a bomb in a suitcase was found on a train traveling from the Basque city of San Sebastian to the capital. Police stopped the train in the northern city of Burgos and removed the bomb.
Richard Evans is editor of "Jane's Terrorism and Insurgency Centre." He told RFE/RL that he would be surprised if yesterday's bombings were an ETA operation. "What makes it surprising is that the group has been hit fairly hard over the last couple of years -- by consistent arrests, seizures of weapons and explosives, numerous terrorist plots have been foiled, and the group really has been on the back foot," he said. "There has been unprecedented cooperation between the Spanish and French authorities, and ETA's supporters and support base in France have also been targeted."
ETA attacks have nearly killed 850 people since the movement began fighting in 1968 for a separate Basque state in northern Spain and southwestern France. But no single attack has approached the carnage of yesterday's events in Madrid.
The group's bloodiest known single bombing to date was in 1987 in a Barcelona supermarket, which killed 21 people. It later apologized for that attack.
A group calling itself the Abu Hafs al-Masri Brigade -- claiming to be affiliated with the Al-Qaeda terror network -- said in an e-mail to the London-based Arabic newspaper "Al-Quds al-Arabi" that it was behind yesterday's attacks in Madrid. The message said Spain was targeted as an enemy of Islam. Spain supported the U.S.-led invasion of Iraq last year.
But the claim has aroused wide skepticism. The group has made a number of unfounded claims in the past, and some terrorism experts doubt whether it exists in more than just name.
Australia's Rohan Gunaratna, author of the book "Inside Al-Qaeda," is among a number of terrorism analysts who point to circumstantial evidence that Muslim terrorists might be involved in the Madrid attacks. "It is a mass casualty and a mass fatality attack," Gunaratna said. "It is a coordinated, simultaneous attack, and it is also an attack on a symbolic target. All the indications are it is an attack not by ETA but by Al-Qaeda."
He notes that Muslim activists have had a significant presence in Spain, adding that Mohammad Atta, the man believed to have led the 11 September 2001, attacks in the United States had often visited Spain.