A top US diplomat on Friday backed Morocco's plan for autonomy in the disputed Western Sahara, calling "serious and credible" during a visit to Rabat."We view Morocco's autonomy plan for Western Sahara as one potential approach to addressing the situation" in the disputed territory, US Deputy Secretary of State John Sullivan told reporters."It is a serious realistic credible plan that is able to satisfy the aspiration of the people of Western Sahara," he said after talks with Moroccan Foreign Minister Nasser Bourita.Morocco and the Polisario Front fought for control of Western Sahara from 1975 to 1991, with Rabat taking over the desert territory before a UN-brokered ceasefire in the former Spanish colony.Rabat considers Western Sahara as an integral part of the kingdom and has proposed autonomy for the resource-rich territory but the Polisario insists on a UN referendum on independence.Diplomatic efforts to end the conflict have been deadlocked since the last round of UN-sponsored talks in 2008.Sullivan's visit coincides with a regional tour of the UN envoy for Western Sahara, Horst Koehler, to push for new talks between Morocco and the Polisario.Morocco maintains that negotiations on a settlement should focus on its proposal for autonomy.Sullivan hailed Morocco as one of Washington's "oldest and closest ally anywhere in the world" and said his government continues to work with Rabat to find a solution to the dispute."We support the UN diplomatic process and effort to find a mutual acceptable political solution to end the conflict that provides for self-determination to the people of Western Sahara, but the most important is our dialogue with the government of Morocco," he said.* Sign up to News24's top Africa news in your inbox: SUBSCRIBE TO THE HELLO AFRICA NEWSLETTERFOLLOW News24 Africa on Twitter and Facebook.