Spain"s high court has served Western Sahara independence leader Brahim Ghali with a June 1 summons for a preliminary hearing in a war crimes case against him, a court document seen by Reuters on Wednesday showed. The summons is the first step toward a potential trial of the Polisario Front leader, whose admittance to a Spanish hospital for treatment last month has angered Morocco. Ghali declined to sign the summons, the document added. A source close to the judicial investigation said he might fail to attend as he might be holding an Algerian diplomatic passport, potentially giving him immunity. News of the summons comes a day after thousands of migrants flocked from Morocco into Spain"s north African enclave of Ceuta. read more Late on Tuesday, Morocco"s minister of state for human rights, El Mustapha Ramid, suggested Rabat had been justified in relaxing border controls there over Ghali"s hospitalisation, though Moroccan police tightened security markedly around the enclave on Wednesday read more Western Sahara is a disputed territory held by Morocco since the mid-1970s, for which the Algeria-backed Polisario Front has been fighting to secure independence since then. Prior to that it was under Spanish control. Ghali and other leaders of the group are accused by human rights groups and Western Sahara individuals of genocide, murder, terrorism, torture and disappearances, the document said. Spain agreed to allow Ghali"s hospitalisation in Logrono, northern Spain, as a "humanitarian gesture". Before this week"s border crisis, Moroccan authorities had warned Spain of repercussions over Ghali"s presence in Spain under a false Algerian passport and an assumed name. Morocco had in recent years worked with Spain, its biggest trading partner, to crack down on migrant flows into Ceuta and another Spanish enclave, Melilla, as well as across the Strait of Gibraltar.