MADRID, May 18, 2008 (AFP) - Over 500 people took part Sunday in a tribute to victims of terrorism in Spain's restive Basque region, just four days after a police officer was killed in a bombing blamed on the separatist group ETA.

In a brief address to the gathering held in the Basque port city of San Sebastian, Basque government leader Juan Jose Ibarretxe called the event a way to 'fight against obscurity' and to remember the toll that terrorism has taken.

Many of the participants were familty member of survivors of attacks carried out by ETA, which is blamed for the deaths of over 800 people in its 40-year campaign for an independent Basque nation.

A van blew up outside a police barracks in the Basque village of Legutiano Wednesday, killing Guardia Civil officer Juan Manuel Pinuel, a 41-year-old father of a young child, and injuring four other police officers.

No one has claimed responsibility for the attack, but police and the government said it bore the hallmarks of ETA.

'We live and die so that Juan Manuel Pinuel's son can live in freedom and peace,' said police officer Leoncio Sainz, who was injured in an ETA attack carried out in the Basque town of Galdacano in October 1984.

Among the other participants at the event was Michael Gallagher, whose 21-year-old son Aidan was one of 29 people killed in an August 1998 car bombing in Omagh, Northern Ireland carried out by the Real IRA faction

Gallagher is spokesman for victims of the attack and their families.

ETA, whose symbol is a snake wrapped around an axe, is considered a terrorist organisation by the European Union and the United States.