World leaders condemned the blasts as an attack on democracy as Interior Minister Angel Acebes said 13 bombs had been placed around Madrid, 10 of which had gone off in and near stations and trains. Security forces detonated three in controlled explosions.
"Three went off at Atocha station" in central Madrid, "four near to" the same station, as well as "one at Santa Eugenia and two at Pozo stations," in nearby suburbs, said Acebes.
Spanish Prime Minister Jose Maria Aznar called crisis talks to discuss the attacks which the government swiftly blamed on the separatist Basque group ETA, although the banned Batasuna political party denied the charge.
The blasts occurred just three days before Sunday's general elections and went off within minutes of each other starting from 7:30am (0630 GMT) as the three Madrid stations were packed with morning commuters.
Rescue workers and passersby
helped the wounded
Acebes said there was "no doubt" the attacks had been carried out by ETA which has led a 36-year campaign for a separatist Basque homeland in which more than 800 people have already died, although the charge was quickly denied by the banned Basque Batasuna party.
Charred and bloodied remains of victims were shown on national television as police, rescue workers and passersby all helped move the wounded.
One Basque nationalist said he did not believe ETA was responsible.
Speaking on Radio Popular in the Basque country, Arnaldo
Otegi, leader of banned radical political party Batasuna, said
he did not believe accusations "even as a hypothesis".
He said the attacks could have been "an operation by sectors
of the Arab resistance".
The Spanish government was a staunch supporter of US President George Bush's decision to go to war in Iraq.
Euskadi ta Askatasuna
Basque separatist group ETA has killed around 850 people since 1968 in its fight for Basque independence and has been a looming presence over the run-up to the Spanish elections.
If ETA is responsible, it would be the worst attack ever by the group, exceeding the 21 killed in a supermarket blast in Barcelona in 1987.
Last month, the separatist group declared a ceasefire limited to the north-eastern region of Catalonia but made clear it would pursue the armed struggle in the rest of the country.
Basques live in the north of Spain
and southern France
Less than two weeks ago police arrested two suspected members who were heading for Madrid with a van containing 500kg of explosives in the run-up to elections.
Thousands of Basques have protested the approaching elections and have called for their banned political party to be put back on the ballot sheet.
Last Saturday's march in San Sebastian sought international attention, highlighting the complete lack of representation for Basque concerns in central government.
Relations between government and local Basque officials have sunk so low the two sides do not talk to each other anymore.
Some are concerned Madrid and Vitoria, the Basque capital, cannot be drawn back together after the 14 March general elections - when a new central government will take over.
The reasons for the rift are clear - Basque hopes for greater self rule, and disagreement on how to deal with the Basque separatist group ETA.
Thousands of Basques called for
self-determination last Saturday
The central government's strained ties with Spain's "autonomous" regions lie at the heart of the election campaign.
Prime Minister Jose Maria Aznar refuses to meet Basque premier Juan Jose Ibarrexte, in large part because of Ibarretxe's proposal to grant the Basque Country a "status of free association" with Spain.
Aznar questions the Basque Nationalist party's loyalty to Spain and its commitment in the fight against ETA.
Meanwhile the Basque Nationalist party, which has governed the region since 1980, sometimes brands Aznar's party as the heirs to former dictator General Francisco Franco, who died in 1975.
"If the Basque government wants a friendly relationship with the rest of Spain, it should reconsider its behaviour of recent years," said Carlos Urquijo, Madrid's representative in the Basque region.
"If you keep giving a kick in the pants to the person you are trying to talk with, you can't expect them to open the door for you," Urquijo said, referring to the so-called "Ibarretxe Plan".