U.N. Secretary General Ban Ki-Moon has said he will try to restart negotiations between Western Sahara’s Polisario independence movement and Morocco to resolve their conflict and allow Sahrawi refugees to return.

The dispute over the arid region in the northwest corner of Africa has festered since Morocco took most of it over in 1975 following the withdrawal of former colonial power Spain.

The Polisario Front, which says the territory belongs to ethnic Sahrawis, waged a guerrilla war until a U.N.-brokered ceasefire in 1991 that did not settle the dispute. The two sides have been deadlocked since.

The U.N. chief plans this weekend to visit refugee camps in Algeria’s Tindouf area where Polisario is based.

Before leaving Mauritania on Thursday, the U.N. chief said he intended to “relaunch negotiations to resolve the conflict so that the Sahrawi refugees can return home to Western Sahara”.

“The patience of the Sahrawi people has now run out. The U.N. has lost its way on Western Sahara,” Polisario leader Mohammed Abdelaziz said in a statement on Friday.

“Ban’s visit and his upcoming reports to the Security Council are the best opportunity in a long time to reset negotiations.”

Polisario, backed by Morocco’s regional rival and neighbour Algeria and a number of other African states, wants to hold a referendum promised in the ceasefire deal on the region’s fate.

“We want to hear from the Secretary-General in order to achieve a solution this year,” Abdelaziz said.

“Allowing the stalemate to continue would have serious consequences not only for the people of Western Sahara, but also for the prospects for peace and security in a Maghreb region.”

Rabat wants Western Sahara, which is rich in phosphates and possibly offshore oil and gas, to be an autonomous part of Morocco and disagrees with Polisario over who should take part in the referendum.

Ban said last year U.N. envoy Christopher Ross had intensified efforts to facilitate the entry of the parties into negotiations “without preconditions and in good faith”.