UNITED NATIONS (Reuters) - The United Nations envoy for the disputed Western Sahara territory has offered his resignation after eight years of trying to bring the Polisario independence movement and Morocco back to negotiations to end their conflict.

Morocco took most of Western Sahara in 1975 following the withdrawal of the 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.

U.N. attempts to hold a referendum on the future of the region have failed since then, with the two sides deadlocked. Christopher Ross has been the U.N. special envoy for Western Sahara since January 2009, when he was appointed by the then U.N. Secretary-General Ban Ki-moon.

U.N. political affairs chief Jeffrey Feltman told reporters on Monday that Ross had offered his resignation.

“He has worked for eight years to try to come up with a framework by which the parties ... would be able to renew negotiations, on an unconditional basis, about the permanent settlement of this dispute,” Feltman said.

“He has been unable to bring the parties back to negotiations and ... he has offered his resignation to the secretary-general for the secretary-general to act upon at a time that he sees fit,” he said.

U.N. Secretary-General Antonio Guterres succeeded Ban on Jan. 1.

Morocco last month announced the withdrawal of its forces from a U.N. buffer zone in the disputed Western Sahara territory, where for months they had been in a standoff with troops from the Polisario independence movement.

The move took place days after a phone call between Morocco’s King Mohammed VI and Guterres, reducing military tensions in Guerguerat, a remote area in Western Sahara near Mauritania.