A powerful car bomb exploded at Madrid's international airport on Saturday, leaving two people missing and injuring 26 in an attack blamed on the Basque separatist group ETA. The bombing ended a nine-month cease-fire and prompted the government to halt plans for negotiations with ETA. "As the conditions that we laid down have not come about, I have ordered the suspension of all initiatives to develop a dialogue," Prime Minister Jose Luis Rodriguez Zapatero said. "The government considers that today's attack is incompatible with a permanent cease-fire." "Today's action is the most mistaken and useless step the terrorists could have taken" said Zapatero. The attack early Saturday inside a multistory parking garage at Madrid's Barajas airport on one of the airports's busiest traveling days of the year was blamed on ETA. "The condition for dialogue was and is the unequivocal desire to abandon violence," said Zapatero. "The very grave attack today by the terrorist band ETA is radically contrary to that desire." said Zapatero. "ETA has taken a road that leads nowhere, that only provokes pain," said Zapatero, who cut short a family holiday to take charge of events. After a warning call from the armed group, a maroon-colored van exploded around 0800 GMT inside the garage adjoining the airport's new Terminal 4, sending a massive column of smoke into the air and collapsing part of the building, sending rubble crashing onto parked cars. Two Ecuadorean men believed to have been sleeping inside a parked car were missing in the rubble and 26 were slightly injured, mostly with damage to their ears from the blast's shockwave. Air traffic at Terminal 4, which is connected to the garage, was halted for several hours but returned to normal by early afternoon, said Interior Minister Alfredo Perez Rubalcaba. Flights were not affected at the other three terminals at Barajas's International Airport. One witness, Renzo Zarzal, 28, a worker at a nearby highway toll booth, said the blast was strong enough to shake some surrounding buildings. "I was outside my booth talking to a colleague when there was a massive blast that really shook us and rattled the roof of the toll complex," Zarzal said. Rubalcaba said the damage to the car park was "extensive" and television images showed a number of floors had collapsed on top of each other, with adjoining staircases left twisted and dangling in mid-air. Rubble had crashed onto numerous cars parked outside the terminal and smoke and dust hung in the air throughout the building, which only opened in February. Firefighters had to tackle several fires following the initial explosion. Many parts of the building looked unsafe and about to collapse. Among the injured, the worst off appeared to be a policeman who received cuts from flying glass. As recently as Friday Zapatero had insisted he was optimistic that ETA's cease-fire would lead to a definite peace process. The outlawed Batasuna party, considered ETA's political wing, considered the process was still alive and more necessary than ever. "For Batasuna, the Basque peace process has not broken down," said Batasuna leader Arnaldo Otegi. "Not only is it not broken but it more necessary than ever," he said. "What happened in Madrid, if it's confirmed ETA is behind it, doesn't take us back to the scenario that existed before March 24 (in reference to the day ETA declared its "permanent" cease-fire)" he said. He blamed Zapatero's government for a breakdown in peace talks between separatists and Madrid. "There hasn't been a gesture, not a single one, from the Spanish government," said Otegi. ETA has not killed anyone since May 2003, but continued a series of low-level bombings until just before the cease-fire. More than 800 people have died since the group took up arms in the late 1960s. ETA and its outlawed political wing, Batasuna, have been demanding - and the government refusing - the start of talks among Basque political parties on the region's future. These would be in parallel to talks between the government and ETA on the nuts and bolts of dissolving the armed militancy. Zapatero said in June he would hold such talks with ETA, but they are not known to have taken place. Pro-ETA street violence that had halted with the truce resumed in earnest in August, and ETA was blamed for a robbery of 300 pistols in France in October. The opposition Popular Party, which has strongly opposed Zapatero's stance, urged the government to break any possible contact with the armed group and to defeat ETA by police and judicial means. "This attack means that ETA is a criminal organization that doesn't want peace" said Popular Party leader Mariano Rajoy.