Three bombs exploded in Spain's Basque region on Thursday, officials said. No one was injured in the blasts, which police said were carried out by the separatist group ETA.

All three blasts, which occurred on the traditional workers holiday of May Day, targeted labor-related government buildings.

Basque regional police said one of the bombs went off in Arrigorriaga near Bilbao and the other two exploded in San Sebastian.

The first bomb targeted a Labor Ministry building and came without warning, police said.

The other two were preceded by a call from someone who claimed to be from ETA, police said. The person warned when and where the bombs would explode, they said.

The San Sebastian bombs were smaller than the first and exploded near a Basque regional government office of an agency that deals with workplace safety, a Basque police official said. He spoke on condition of anonymity because of department rules barring him from giving his name.

ETA declared a cease-fire in March 2006 but ended it in December of that year after failing to win concessions in talks with the government.

The group has killed more than 800 people in its decades-old struggle to create an independent Basque homeland in northern Spain and southwest France.

ETA's last fatal attack was the shooting of a former town councilor in the Basque region two days before a Spanish general election on March 9.