Updated on Saturday, October 04, 2008, 00:00 IST

Tolosa (Spain), Oct 04: A bomb exploded outside a court house in Spain's northern Basque region on Saturday, causing considerable damage but no injuries, regional police said.

The detonation in the town of Tolosa was preceded by a telephone warning to a regional road rescue service by a man who said he spoke on behalf of Basque separatist group ETA.

The caller said a bomb would explode by the court house at IST 0645 (1:15 local time) today. Officers rushed to the scene where they found a rucksack and proceeded to cordon off the area, a police statement said. The rucksack exploded at the announced time and blew a large hole in the courthouse, breaking glass all around the building and damaging cars.

As an organization, ETA normally doesn't claim responsibility for its attacks until weeks after they occur.

On September 22, ETA used a large car bomb to kill Sgt Maj Luis Conde de la Cruz, 46, an off-duty soldier who was on vacation at an army seaside retreat in the northern city of Santona. That attack was the third powerful car bomb attack in Spain in a 24-hour period and signalled a new ETA offensive. It came days after the Spanish Supreme Court outlawed two Basque pro-independence parties on the ground that they were linked to ETA.

ETA has conducted a violent campaign, including shootings and bombings, since 1968 in an effort to create an independent Basque state in northern Spain and south-western France. It has killed more than 825 people.

ETA declared a cease-fire in March 2006, but reverted to violence in December of that year after peace talks with the government failed. The group - considered a terrorist organization by Spain, the EU and the US.

Bureau Report