Andoni Zengotitabengoa Fernandez, 32, was arrested in March last year at Lisbon airport for trying to travel to Caracas with a fake passport.

A month earlier, police discovered 300 kilograms of explosives ready for use, as well as 800 kilograms of equipment and material including 500 kilograms of ammonium nitrate from a hastily abandoned villa in the central region of Obidos.

Fernandez was accused of being one of the co-tenants of the villa. He has a long crime record ranging from aggravated robbery and fraud to possession of illegal weapons.

ETA is blamed for the deaths of 829 people in its four-decade campaign of bombings and shootings to force the creation of a Basque homeland in northern Spain and southwestern France.

The group, weakened after years of arrests of its senior leaders, has not committed an attack on Spanish territory since August 2009.

Spanish authorities believe ETA has started to move its logistical operations from France to Portugal.

In January 2010, two other presumed ETA members — a man and a woman — were arrested in northern Portugal after avoiding a check by Spanish police.