Rabat, Morocco  - US President George W Bush has written to Morocco's King Mohammed VI, expressing support for Morocco in its conflict with the Western Saharawi independence movement Polisario Front, a Moroccan government source announced Friday.

The United States had the "clear national" position of seeing Morocco's autonomy offer to Western Sahara as the "only possible solution" to the decades-long conflict, the source quoted Bush as writing.

"An independent state in the Sahara is not a realistic option," while the Moroccan proposal of granting the region a substantial degree of autonomy instead of independence was "credible and serious," Bush was further quoted as saying.

Morocco annexed Western Sahara after the colonial power Spain withdrew from there in 1975. Polisario then launched a guerrilla war which ended in a ceasefire brokered by the United Nations in 1991.

The UN plan foresaw a referendum on independence which has not been held. Polisario continues insisting on the referendum, and has threatened to take up arms again if the original UN plan is not complied with.

Bush called on Morocco and Polisario to become deeper involved in the ongoing negotiations to solve the conflict. (dpa)