Senior leaders from the European Union, including British Prime Minister Tony Blair and French President Jacques Chirac, rubbed shoulders with Spanish King Juan Carlos, Queen Sofia, representatives of several other European royal households and US Secretary of State Colin Powell under tight security.

Morocco's royal family was also represented, with Prince Moulay Rachid, the younger brother of King Mohammed VI, in attendance.

At least six of 13 people currently in detention on suspicion of involvement in the bombings are Moroccan nationals, of whom at least one linked to last year's bombings in Casablanca.

Blair had earlier met Spanish Prime Minister-elect Jose Luis Rodriguez Zapatero for an hour of talks. The two are on opposing sides of the debate over the US-led war in Iraq, which Blair roundly supported, while Zapatero has sharply criticised it and threatened to withdraw Spanish forces serving there by the end of June.

Many Spaniards see Spanish support for Washington and London over the conflict as the underlying reason why suspected Islamic extremists targeted Madrid in what they regard as an act of vengeance for the foreign policy of outgoing Prime Minister Jose Maria Aznar.