A bomb detonated at a rail station outside the Basque city of Bilbao early Monday, causing serious damage and igniting a fire, Basque police said. No one was injured.

The device exploded in Barakaldo, a town on the outskirts of Bilbao, Basque regional police said.

The blast occurred about half an hour after midnight and bore the hallmarks of the kind of attack waged by young supporters of the armed separatist group ETA. But a Basque police official said it was too early to say who was behind the explosion.

On Sunday police detained 18 fugitive members of an outlawed Basque youth group which the Supreme Court ruled last month is a terrorist organization because of its alleged links to ETA.

Spanish National Radio suggested the bomb blast on Monday might be in reprisal for these arrests.

The explosion set off a fire inside the station, which handles commuter trains. Firefighters worked for several hours to extinguish the blaze, and rail service was halted until it was put out.

The explosion blew out doors and windows and sent them flying 10 yards from the building, Barakaldo Mayor Tontxu Rodriguez said, according to the Internet edition of the newspaper El Pais. He said it was the third time the station had been attacked.

"But this is not the path to peace and freedom. All this does is to disrupt the everyday lives of citizens," the paper quoted Rodriguez as saying.

ETA detonated a massive bomb at Madrid airport on Dec. 30, killing two people and ending a nine-month cease-fire. The attack prompted the government to halt plans for negotiations with ETA.