Madrid, Spain ? A car bomb blamed on Basque separatists exploded Wednesday in a Madrid office park near where King Juan Carlos later appeared, injuring at least 43 people in the worst terrorist attack in the Spanish capital since last year’s bombing of commuter trains.

The bomb exploded about 9:30 a.m., less than an hour after a warning call purportedly made by the Basque separatist group ETA. It shattered thick panes of glass in buildings — spraying shards over a wide area — and damaged cars.

Police did not have time after the call to the Basque newspaper Gara to fully cordon off the area or fully evacuate workers and visitors at the sprawling convention center nearby, where the king later met Mexico President Vicente Fox to inaugurate an art show that includes Mexican works.

The bomb used an estimated 66 pounds of explosives, Interior Minister Jose Antonio Alonso said. It was the worst blast in Spain’s capital since the March 11 train bombings that killed 191 people and were claimed by militants saying they acted on behalf of al-Qaida.