Up to two million people have taken part in a demonstration against terror in the Spanish capital Madrid a day after bomb attacks killed nearly 200.
Huge crowds ignored the rain to express their rejection of violence
European leaders joined the protest to show solidarity.
Millions more Spaniards joined similar rallies and vigils held across the country, which remains in mourning.
Officials say Basque militants from Eta remain the main suspects - but Basque media are carrying a statement, said to be from the group, denying involvement.
The government says it is ruling out no line of inquiry. Some clues appear to implicate Islamic radicals.
Prince, politicians and people
In Madrid huge crowds have been marching despite heavy rain - clutching umbrellas, flags and posters denouncing terrorism.
Members of Spain's royal family including Crown Prince Felipe, and his sisters Princess Elena and Princess Cristina joined Prime Minister Jose Maria Aznar to head the demonstration.
They were joined by European allies - Silvio Berlusconi of Italy, Jean-Pierre Raffarin of France as well as their Irish counterpart Bertie Ahern and Romano Prodi representing the European Union.
John Prescott, the UK deputy prime minister, and German Foreign Minister Joschka Fischer also participated in the march.
A six-lane motorway through the capital was closed off to allow demonstrators to march to the railway station at Atocha - where the worst of the attacks took place.
Some chanted: "Assassins", "A people united will never be defeated".
Others simply stood quietly in the rain.
One woman at the Madrid rally told the BBC: "I wanted to feel a little bit better, because at home I can't do anything."
She added: "Everyone here in Madrid knew someone who died yesterday, and that feels worse."
About 1,400 people were injured in the 10 blasts on commuter trains in the morning rush hour. Some remain in a critical condition.
Correspondents say the entire nation is still in shock. Three days of national mourning are being observed with flags at half-mast, public institutions closed and political campaigning cancelled ahead of Sunday's general election.
Reports from outside the capital say vigils and rallies brought more than six million other people out onto the streets of towns and cities - including those in the Basque country, where local rivalries have been forgotten for now.
But even as the millions stood as one against the violence, it was still not clear who had ordered the attacks.
Interior Minister Angel Acebes on Friday said the militant Basque separatist group Eta remained the government's prime suspect.
The group has previously targeted the Spanish railway system and two Eta suspects were arrested last month driving a truck loaded with explosives headed for Madrid.
However there has been speculation about a possible connection with Islamic militants.
A stolen van found near the route of the trains contained detonators and a recording of Koranic verses, the interior minister said.
A message purportedly from the Abu Hafs al-Masri Brigades was also sent to a UK-based Arabic newspaper saying it had attacked "America's ally in its war against Islam" on behalf of al-Qaeda.
Spanish editorial writers are demanding answers before voters go to the polls on Sunday, because the culprits' identity might influence people's choice of party.
The ruling Popular Party campaigned on a hardline stance against Eta but also defied popular opposition by supporting the US-led war against Iraq - which may have triggered an attack by al-Qaeda.
Thursday's attack was the worst act of terrorism in modern Spanish history and the deadliest in Europe since the Lockerbie airliner bomb killed 270 in 1988.
It has been condemned by leaders around the world, who have pledged their support for the Spanish people.
1. Atocha station, 0639 GMT: Three blasts on a train inside the station kill at least 34 people. Four blasts on a train 500m outside the station kill at least 62 people
2. El Pozo station, 0641: Two bombs explode on a double-decker train killing at least 70 people
3. Santa Eugenia station, 0642: A bomb explodes on a fourth train in the station, killing at least 17 people