Police say a bomb has exploded outside the offices of Spain's ruling Socialist party in a Basque town in northern Spain, causing considerable damage. No one was injured.

Basque police say in a statement that the bomb exploded at 3:25 a.m. Sunday in Elgoibar, following a telephone warning in the name of Basque separatist group ETA.

The warning was received by emergency road services and police cordoned off streets and evacuated residents after finding a suspicious package.

Police say around 3 kilograms of explosives seriously damaged the offices, caused damage to parked cars and broke windows along the street.

Another bomb attributed to ETA exploded four days ago in a working-class neighborhood of Bilbao, gutting a Socialist Party office.