Madrid - A bomb exploding at a train station in Spain's northern Basque Country early Saturday morning caused heavy damage, but no injuries, officials said.

The bomb exploded at about 0:30 am local time (2230 GMT Friday) at the Berriz train station, causing considerable damage. Officials said that there had been no warning, and no one claimed immediate responsibility for the bomb.

The militant Basque separatist group ETA usually warns in a phonecall shortly before a bomb it has planted goes off.

The train line, run by Eusko Tren, links Berriz with the cities San Sebastian and Bilbao.

Two hours after the blast, a group of "radicals" hit a train station in Amorebieta, run by the same company, with molotov cocktails, also causing damage, police said.

ETA is blamed for more than 820 deaths in its four-decade campaign for a sovereign Basque state. (dpa)