Spanish paramilitary police have arrested five suspected members of ETA and seized 220 pounds of explosives.
The five were arrested in raids in the northern coastal city of San Sebastian and the towns of Billabona and Ibarra.
National radio said police had confiscated explosives, a machine gun, several smaller guns and computer material.
The radio said the detainees were also being investigated for possible links to last Thursday's murder of a Socialist party town councillor in the Basque region. Authorities blamed ETA for the death.
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ETA has admitted killing more than 800 people since it took up arms for Basque independence in 1968. The group is classified as a terrorist group by the EU and the United States.