More than 175,000 people in Spain's Basque Country joined to form a 202 kilometer-long human chain on Sunday, as they called for the right to host a referendum on independence form Madrid.
The chain extended from the city of San Sebastian all the way to the Basque parliament in Vitoria-Gasteiz, the capital of the autonomous region.
The protest was organized by the Basque group Gure Esku Dago (In Our Own Hands).
The Basque Country enjoys higher levels of self-determination than any of Spain's other sixteen regions, with its own police force, education system, language and special financial arrangement with Madrid.
While polls suggest that a vast majority of Basque people do not support full independence (only around 15 percent back total secession from Madrid), many nevertheless believe that the people should have the right to vote on the issue.
Read more: In final letter to Spain, Basque separatists ETA end 'all political activity'
Spanish laws block secessionist push
However, the Spanish government and the constitutional court maintain that any regional plebiscite on independence is illegal.
The Spanish Constitution, created in 1978 following the end of General Francisco Franco's dictatorship, states that the country is indivisible, referring to the "indissoluble unity of the Spanish Nation."
Last year's attempts by the Catalan government to hold an independence vote were met with a brutal crackdown by Spanish security forces. Catalonia's subsequent declaration of independence prompted Madrid to take temporary control of the regional parliament and detain dissident civil servants who took part in the vote.
Read more: Catalan independence - What you need to know
Spain's former conservative prime minister, Mariano Rajoy, was widely criticized for his handling of the Catalan crisis. He was replaced by Socialist leader Pedro Sanchez after a no confidence vote on June 1 — a move backed by the autonomous Basque and Catalan governments.
Since taking power, Sanchez has indicated that he favors a more federal approach and that he would be willing to amend the constitution to grant the autonomous regions greater self-determination. However, he was stopped short of advocating for Catalonia or the Basque Country's right to full secession.
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