Protesters calling for independence from Morocco were chased through the streets of the city, and some Spanish activists were arrested.
By nightfall, the demonstrations had spread to other neighborhoods of the city and degenerated into stone throwing clashes between youths and police.
Local hospitals said at least 90 protesters were injured, and the governor’s office said 35 members of the security force were hurt.
A foreign journalist on the scene was stopped several times by police to prevent him from covering the protests and nearly had his camera taken away.
Western Sahara is a disputed territory in North Africa, bordered by Morocco to the north, Algeria to the extreme northeast, Mauritania to the east and south, and the Atlantic Ocean to the west.
The European Union parliament recently approved a four-year agreement giving its fleet access to Moroccan waters for 40 million euros ($55 million) a year. The richest fishing waters are off the coast of the Western Sahara, which was annexed by Morocco in 1975.
Activists in the disputed territories say Morocco has no right to enter into treaties concerning their national resources and lobbied against the accord, which was approved by the EU parliament in a 310-to-204 vote, with 49 abstentions.
In December 2011, the parliament let lapse an earlier fishing agreement, partly over concerns about the situation in the disputed territories.
Morocco declares the Western Sahara an integral part of its national territory, but the U.N. is supposed to organize a long-delayed referendum to allow the inhabitants to vote on their fate.
The desert region is also rich in phosphates, and international companies have started looking for off-shore oil deposits.
Unlike in the rest of Morocco, demonstrations are not tolerated in the restive towns of Western Sahara, which are under heavy security.
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