By John Hooper

The United Nations Security Council on Sunday night extended the UN mandate to keep the peace in the disputed Western Sahara only until February 11. The decision was the latest indication of international exasperation with the lack of progress towards solving Africa's last decolonisation wrangle.

It is 23 years since Morocco invaded the former Spanish colony, setting off a war that has left around 165,000 refugees stranded in an expanse of desert more than 1,000 miles south of Algiers.

The UN secretary-general, Kofi Annan, had asked for his peacekeeping force's mandate to be extended until the end of February. This was to allow time for Morocco to prepare the latest changes to arrangements for a referendum on the territory's independence or integration into Morocco. But in an apparent effort to exert pressure on Rabat, the Security Council refused last Thursday to authorise the UN force, known as MINURSO, beyond the end of next week.

The struggle for the Western Sahara is the UN's second longest running dispute. Only the stand-off between Greece and Turkey over Cyprus has proved more intractable. Guerrillas of the Algerian-backed Polisario Front fought a 15-year war for Saharan self-determination until the UN brokered a ceasefire in 1991. Fighting stopped on the understanding that the sides would put their claims to a popular vote. But the proposed referendum has been postponed repeatedly as Morocco has tried to swell the list of eligible voters with people the Saharawis claim are not from their territory.

Last September a UN identification commission completed the task of sifting through some 147,000 would-be voters. Saharawi sources said the number had been whittled down to around 85,000. Two months later, in a significant policy shift, the Polisario Front agreed to Mr Annan's proposal that the commission should also scrutinise a further 65,000 potential electors. The Polisario Front's unexpected readiness to compromise has undermined King Hassan's government. 'Now that we are saying 'yes,' the Moroccans have been left without any excuses,' a Saharawi official said.

Mr Annan told the Security Council in a report last week that the Moroccans 'expressed concerns and sought clarification'. His representatives had provided 'extensive clarification', but Rabat 'intended to propose in writing specific amendments to the texts of the protocols'.

The secretary-general has staked his personal credibility on the package he has submitted and it is clear that he would favour a more vigorous approach if it does not succeed. His report even hinted at an end to the UN's peacekeeping mission, which would probably lead to a resumption of war. He said in his report that, should the prospects for a settlement 'remain elusive at the time of the submission of my next report, it would be my intention to ask my personal envoy to reassess the situation and the viability of the mandate'.

The United Nations first called for independence for what was then the Spanish Sahara as long ago as 1965. Ten years later King Hassan of Morocco ordered 350,000 volunteers to cross into the territory on what was called the Green March.