An explosion took place at a train station at Lutxana in Spain's Basque region early hours this morning.
No one was injured in the attack. Police are investigating whether it was the work of separatist group Eta or violent Basque pro-independence street gangs, the regional government's interior minister said.
No group has claimed responsibility for the explosion which left the station burning for more than three hours.
ETA broke a nine-month ceasefire on December 30th by exploding a powerful car bomb at Madrid airport that killed two people.
Today's blast could also be the latest act of violence by pro-independence street gangs, who have attacked police and set fire to buses, cars and cash machines in the Basque region in recent months, even during Eta's ceasefire.
The station has come under attack several times before.