By Pascale Harter BBC correspondent in Rabat

The Polisario demands outright independence

He is recommending a UN mission in the area is extended to give Morocco longer to consider a UN-brokered solution.

The Saharawi government-in-exile, the Polisario, has accepted the US plan for the former Spanish colony, annexed by Morocco in 1975.

Mr Annan is believed privately to be at the end of his tether over the issue.

Technically it is Africa's longest-running war - between the Polisario and Morocco.

And over what? A vast, unchanging landscape of barren sand, the western Sahara.

Lucrative

It might be just a big beach but it is a beach with lucrative fish stocks and suspected oil deposits.

Despite being a highly inhospitable place to live, neither the Polisario nor Morocco are eager to give it up.

That is why UN mediation - what Kofi Annan himself has described as a "zero sum game" or one with no winners - is continuing.

For almost a quarter of a century the UN has kept a monitoring force in the area, ready to implement an ever-imminent referendum on independence.

But in all that time the two sides have never been able to agree on the fine print of that referendum.