A series of bombs hidden in backpacks exploded in quick succession Thursday, blowing apart four commuter trains and killing at least 192 people and wounding 1,200. Spain blamed Basque separatists but a shadowy group claimed responsibility in the name of al-Qaida for the worst terrorist attack in Spain's history.

Panicked commuters trampled on each other, abandoning their bags and shoes, after two of the bombs went off in one train in the Atocha station in the heart of Madrid. Train cars were turned into twisted wrecks and platforms were strewn with corpses. Cell phones rang unanswered on the bodies of the dead as frantic relatives tried to call them.

"March 11, 2004, now holds its place in the history of infamy," Prime Minister Jose Maria Aznar said.

The bombing came three days ahead of Spain's general election on Sunday. A major campaign issue was how to deal with ETA, the Basque militant group.

Campaigning for the election was called off and three days of mourning were declared.

It was also 2 1/2 years after the Sept. 11, 2001, terrorist attacks in New York and Washington, and was Europe's worst since the bombing of a Pan Am jetliner over Lockerbie, Scotland, in 1988 killed 270 people,

The 10 backpack bombs exploded in a 15-minute span, starting about 7:39 a.m., on trains along nine miles of commuter line from Santa Eugenia to the Atocha terminal, a bustling hub for subway, commuter and long-distance trains just south of the famed Prado Museum. Police also found and detonated three other bombs.

"An act of barbaric terrorism has engulfed Spain with profound pain, repulsion and anger," King Juan Carlos of Spain said on national television.

Worst hit was a double-decker train at El Pozo station, where two bombs killed 70 people, fire department inspector Juan Redondo said. One corpse was blown onto the roof.

At the Santa Eugenia station, "there was one carriage totally blown apart. People were scattered all over the platforms. I saw legs and arms. I won't forget this ever. I've seen horror," said Enrique Sanchez, an ambulance worker.

Forty coroners worked to identify remains, the national news agency Efe said, and a steady stream of taxis carried relatives to a sprawling convention center that was turned into a makeshift morgue.

The government called for nationwide anti-ETA rallies for Friday evening, and millions were expected to attend. Three days of national mourning were declared.

Who carried out the highly coordinated attack was a mystery. The Spanish government put the Basque separatist group ETA at the top of its list of suspects, although a shadowy group claimed responsibility in the name of al-Qaida.

The Arabic newspaper Al-Quds al-Arabi said it had received a claim of responsibility issued in the name of al-Qaida. The e-mail claim, signed by the shadowy Brigade of Abu Hafs al-Masri, was received at the newspaper's London offices and said the brigade's "death squad" had penetrated "one of the pillars of the crusade alliance, Spain."

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

Spain had backed the U.S.-led war on Iraq despite domestic opposition, and many al-Qaida-linked terrorists have been captured in Spain or were believed to have operated from there.

Spain's government is studying the reported al-Qaida claim but still believes ETA is more likely responsible, a senior official in Aznar's office said.

Spain's security forces were not ruling out "any line of investigation," Interior Minister Angel Acebes said.

The United States believes Al-Masri sometimes claims to be acting on behalf of al-Qaida, and it later turns out they were not. For example, they took credit for blackouts in the United States and London last year.

A U.S. counterterrorism official, speaking on condition of anonymity, said it was too early to determine who was responsible. The official noted that al-Qaida usually does not take responsibility for attacks.

If the attack was carried out by ETA, it could signal a radical and lethal change of strategy for the group that has largely targeted police and politicians in its decades-long fight for a separate Basque homeland.

But after police found a stolen van with seven detonators and the Arabic-language tape parked in a suburb near where the stricken trains originated, Interior Minister Angel Acebes said: "I have just given instructions to the security forces not to rule out any line of investigation."

A top Basque politician, Arnold Otegi, denied ETA was behind the blasts and blamed "Arab resistance," noting Spain's support for the Iraq war.

The government said ETA had tried a similar attack on Christmas Eve, placing bombs on two trains bound for a Madrid station that was not hit Thursday.

"ETA had been looking for a massacre," said Acebes, the interior minister. "Unfortunately, today it achieved its goal."

The Interior Ministry said tests showed the explosives used in the attacks were a kind of dynamite normally used by ETA.

The bombers used titadine, a kind of compressed dynamite also found in a bomb-laden van intercepted last month as it headed for Madrid, a source at Aznar's office said, speaking on condition of anonymity. Officials blamed ETA then, too.

In a break with past ETA tactics, there were multiple attacks and no advance warning. ETA has usually gone after one target at a time and the largest casualty toll was 21 killed in 1987.

ETA has claimed responsibility for more than 800 deaths since 1968.

Sympathy poured in from capitals worldwide, led by Spain's partners in the 15-nation European Union, and neighboring France raised its terror alert level. The United States, Britain and Russia said the attacks demonstrated the need for toughened resolve against terrorists.

"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," said President Bush, who spoke by telephone with Aznar.

Aznar was a staunch supporter of U.S.-led war that ousted Saddam Hussein and Spain sent 1,300 troops to Iraq.

Aznar, who himself survived a car bombing in 1995, will step down when a new government is formed after the elections.

Revulsion over the attack could benefit Aznar's ruling conservative Popular Party because of its hard-line stance against ETA.

Both the Popular Party and the opposition Socialists ruled out talks with ETA during the campaign.

"No negotiation is possible or desirable with these assassins who so many times have sown death all around Spain," Aznar said.

The Socialists came in for withering criticism during the campaign because a politician linked to the Socialist-run government in the Catalonia region, which also has separatist sentiment, admitted meeting with ETA members in France in January. The Socialists were lambasted as allegedly undermining Spain's fight against ETA.

The group - Euskadi ta Askatasuna, or Basque Homeland and Freedom - is believed by police to number perhaps only several dozen hard-core militants who are supported by a wider group of Basque nationalists.

The government had recently expressed cautious optimism that ETA was near defeat after mass arrests of alleged members, seizures of weapons and explosives, increased cooperation from neighboring France and the banning of ETA's purported political front. The number of people killed in ETA attacks dropped to three last year.