MADRID, March 11 — Ten nearly simultaneous explosions tore through four packed commuter trains in Madrid during rush hour Thursday morning, killing at least 190 people and wounding nearly 1,500 in the worst terrorist attack in modern Spanish history, three days before national elections.

The explosives were placed in backpacks and left aboard trains and on tracks at three stations. Witnesses describing the scenes of chaos and carnage said they heard multiple explosions at the city’s busy Atocha station, which sent passengers scrambling in a panic. A makeshift emergency hospital was set up alongside the tracks at the station, just south of the Prado Museum. Buses were hurriedly converted into ambulances. The walking wounded were asked to make it to hospitals on their own, and leave vehicles available for the more severely injured.

Prime Minister Jose Maria Aznar called the attacks “a mass murder” and compared them to the Sept. 11, 2001, terrorist strikes in the United States. “March 11, 2004, now occupies a place in the history of infamy,” he said.

Government officials and the media immediately blamed the attacks on the Basque separatist group ETA, which has fought for more than 30 years against the Spanish government.

Later Thursday, however, the Spanish interior minister, Angel Acebes, said the government was investigating a possible link to Islamic extremists after a van was discovered on the outskirts of Madrid carrying seven detonator caps and a cassette tape in Arabic containing verses from the Koran. The van was parked in the town of Alcala de Henares about 15 miles east of Madrid, where at least three of the targeted trains originated.

“I have given our security forces instructions not to rule out anything,” Acebes said, adding that he still considered ETA the principal suspect.

The discovery of the van was followed by a report from London by the Arabic language Al-Quds Al-Arabi newspaper that it had received an e-mail from an Islamic militant group claiming responsibility for the attacks.

“This is part of settling old accounts with Spain, the crusader, and America’s ally in its war against Islam,” the letter said, claiming that it had been sent on behalf of the Abu Hafs al-Masri Brigades, a group aligned with the al Qaeda terrorist network. The letter also said preparations for an attack on the United States were underway.

Spain has worked closely with the United States in the war against terrorism and has 1,300 troops in Iraq. Spanish officials have also rounded up al Qaeda suspects believed to be operating a terrorist cell in the country.

In October, Osama bin Laden, the leader of al Qaeda, warned in an audiotape that countries, including Spain, that cooperated with the United States risked being targeted.

The Aznar government’s support for the Iraq war was deeply unpopular among citizens, with polls indicating that 90 percent of the population was against it. Spain’s involvement in Iraq had become a campaign issue, with the opposition Socialist Party promising to reverse the policy and bring troops home.

After the attacks, President Bush expressed “deepest sympathies” to Aznar and King Juan Carlos. “We stand strongly with the people of Spain,” Bush said. “I appreciate so very much the Spanish government’s fight against terror, their resolute stand against terrorist organizations like the ETA.”

While the Aznar government’s close ties to the Bush administration over Iraq have received little approval, its stance against ETA has been highly popular. The candidate of the governing Popular Party, Mariano Rajoy, has promised to continue the policy pursued by Aznar, who is stepping down after eight years in power. Rajoy’s campaign had tacitly accused his Socialist challenger, Jose Luis Rodriguez Zapatero, of being softer on terrorism.

At Spain’s insistence, the U.N. Security Council swiftly adopted a resolution condemning the attack and accusing ETA of carrying it out. After the vote, Spain’s deputy ambassador, Ana Maria Menendez, declined to explain why officials had eliminated al Qaeda or other groups as potential perpetrators.

(Via The Washington Post)