The Spanish-language website Free WikiLeaks said protests were scheduled to be held in Madrid, Barcelona, Valencia and Seville and at least three other Spanish cities.
The website also said demonstrations were planned Saturday in Amsterdam, the Netherlands, and in the capital cities of Colombia, Argentina, Mexico and Peru, as well as in São Paulo, Brazil. Julian Assange is currently detained in the UK for an alleged crime of sexual abuse.
"We seek the liberation of Julian Assange in United Kingdom territory," the organization said on the website. It urged protesters to gather at 6 p.m. in Spanish cities.
Assange remains in a British jail awaiting a hearing Decembert 14th at which he plans to fight Sweden's request to extradite him to face sex crimes allegations there.
One of his lawyers denied media reports that Assange was being held in isolation at Wandsworth Prison in London.
"He told me he had single cell," Mark Stephens said. He has the ability to watch TV with other prisoners which he does not do because he hates daytime telly. He takes his meals with other prisoners.
Stephens said lawyers met with Assange at the prison for an hour Thursday to prepare for next week's hearing.
The Free WikiLeaks website also calls for "the re-establishment of the WikiLeaks Internet domain," and the restoration of Visa and MasterCard credit card services to enable the "freedom to move money" because no one has "proved Assange's guilt," or charged WikiLeaks with any crime.