(Xinhua) -- Spanish police on Sunday arrested 18 members of three organizations linked to separatist group Basque Homeland and Freedom (ETA) in the northern city of Bilbao in accordance with a court order, local media reported. The 18 detained were among a total of 23 suspects that the country's Supreme Court ordered to arrest as they belonged to three terrorist organizations -- Segi, Jarrai and Haika, all linked to ETA as ruled by the court on Jan. 19. Four had been detained by police earlier. Police made the latest arrest at a court in Bilbao after a Segimeeting, which was also attended by some senior leaders of Batasuna, an ETA political wing. ETA, formed in 1959, has called for the establishment of an independent Basque state in the Basque region straddling the Spanish-French border. Over the past four decades, assassinations, kidnappings and explosions carried out by the group have claimed the lives of nearly 1,000 people. The European Union and the United States have listed ETA as a terrorist organization. ETA declared a permanent truce on March 22, 2006. Three months later, the Spanish government decided to start a dialogue with the group.