MADRID, July 4, 2008 (AFP) - A small blast struck a telecoms relay station in Spain's northern Basque region Friday, causing material damage but no injuries, said police and regional government officials who blamed the Basque separatist group ETA for the attack.

The bomb, which contained between three to five kilogrammes (11 pounds) of a still unknown type of explosive, went off in the town of Barrundia at around 2:00 am (0000 GMT), a Basque government spokesman told AFP.

The explosion caused 'important damage to the exterior wall' of the station, he added.

It is the fourth bombing of a relay station by suspected separatists so far this year, according to the Vasco Press news agency.

ETA is blamed for over 800 deaths in Spain in its 40-year campaign for Basque independence.

It declared a unilateral ceasefire in March 2006, raising hopes for an end to the violence. But an ETA bombing at Madrid's airport in December 2006 that killed two men put an end to tentative peace talks with the government.

ETA officially terminated the ceasefire in June last year, and since then the government has blamed it for four killings.