MADRID, Dec. 31 (Xinhua) -- Spanish authorities have identified a young Spaniard who was being held hostage for three days by the separatist group ETA, as the owner of the van used in a car bomb attack in Madrid's Barajas airport on Saturday morning, police said on Sunday.

    Police did not name the van owner, who was kidnapped on Wednesday by three hooded men in Luz-Ardiden, France, where he had traveled for a camping and skiing holiday.

    The victim, a native of Ordizia, in the northern Spanish region of Guipuzcoa, was released a few hours after the attack on Saturday.

    Investigations showed that the van, loaded with around 500 kg to 800 kg of explosives, was parked on the second floor of the car park on Friday night.

    The blast, which ended a nine-month ceasefire by the armed separatist group and let the government suspend efforts to broker a negotiated solution to a four-decade conflict, left two young Ecuadorians missing and 19 people slightly injured.

    The blast seriously damaged the parking lot and caused a brief disruption of the airport's operation. ETA claimed responsibility for the attack in one of three early morning anonymous telephone calls.

    Thousands of Spaniards took to the streets on Sunday to protest the bombing.

    Madrid city authorities called off a planned light and sound fiesta at the central Puerto del Sol square, where Spaniards and tourists traditionally get together to celebrate the new year.

    ETA, an abbreviation for Basque Homeland and Freedom, which was formed in 1959, has called for the establishment of an independent Basque state in the Basque region straddling the Spanish-French border.

    Over the past four decades, assassinations, kidnappings and explosions carried out by the group have claimed the lives of nearly 1,000 people. The European Union and the United States have listed ETA as a terrorist organization.

    ETA declared a permanent truce on March 22. Three months later, the Spanish government decided to start a dialogue with the group.