MADRID (Reuters) - Simultaneous bomb blasts ripped through packed commuter trains at three stations in Madrid on Thursday, killing 182 people and injuring about 900 in Europe's bloodiest attack for more than 15 years.

There was no immediate claim of responsibility for the 10 rush-hour blasts three days before Spain votes in a general election, but Prime Minister Jose Maria Aznar's government blamed the Basque separatist group ETA.

Officials brushed aside suggestions Muslim militants angry at Spain's support for the U.S.-led war in Iraq could have been behind the bombs, which tore people including a baby to shreds, and left pools of blood on wrecked trains, tracks and buildings.

"It is absolutely clear that the terrorist organization ETA was seeking an attack with wide repercussions," Spanish Interior Minister Angel Acebes told a hastily called news conference.

U.S. intelligence agencies said it was too early to decide who was behind the attack, but saw the hallmarks of both ETA and Osama bin Laden's al Qaeda.

"There are characteristics of each. You have multiple attacks, multiple explosions in different locations in a short period of time which is very al Qaeda-ish," said one U.S. official, who declined to be identified.

"The train was cut open like a can of tuna... We didn't know who to treat first. There was a lot of blood, a lot of blood," said ambulance driver Enrique Sanchez, at Atocha station in central Madrid.

Passenger Ana Maria Mayor's voice cracked as she told reporters: "I saw a baby torn to bits."

The other blasts occurred at El Pozo station in southern Madrid and at Santa Eugenia in the southeast of the capital.

Aznar called on Spaniards to take to the streets on Friday in protest at the attack, and vowed the government would arrest the "criminals" behind it.

FIGHT FOR SECESSION

ETA (Euskadi ta Askatasuna) has killed around 850 people since 1968 in its fight for a separate Basque homeland in northwest Spain and southwest France, and has been branded a terrorist group by the United States and the European Union.

Late last month, police arrested two suspected ETA members heading for Madrid with a van containing 1,100 lb of explosives, averting a possible attack.

If the Basque group was responsible for Thursday's bombings, it would be its deadliest attack, far exceeding the 21 people it killed in a supermarket blast in Barcelona in 1987.

It was the biggest death toll in an attack in Europe since December 1988, when a Pan American World Airways Boeing 747 crashed on the town of Lockerbie, Scotland, killing all 259 aboard after a bomb on the plane exploded. Eleven people in the town were also killed.

The Spanish government convened an emergency cabinet meeting and the ruling Popular Party suspended its election campaign, which had focused on a tougher stance against ETA.

European stock markets fell sharply on fears that the attack was the work of Islamic extremists, while bond markets rallied as investors pushed their cash into safe havens. The September 11 attacks on the U.S. led to sharp falls in global markets in 2001 and were blamed for deepening a worldwide economic slump.

President Bush joined other leaders in condemning the bombings.

Some experts on ETA said the bombings did not fit the group's usual profile for attacks. ETA has frequently warned in advance of its attacks.

Last month ETA declared a cease-fire limited to the northeastern region of Catalonia.