North Africa Correspondent Heba Saleh: "The real hurdle for Mr Annan will be convincing the Moroccan authorities."

Mr Annan was speaking after talks in the Western Sahara with the Polisario Front, who are fighting for the independence of the territory.

However, he said that the Moroccans had raised some questions.

The Western Sahara was taken over by Morocco after the Spanish pulled out in the 1970s.

"We are discussing these questions which I hope we will be able to clarify," Mr Annan said.

A crucial vote

The UN has been trying to organise a referendum on the future of Western Sahara for seven years, but it has been repeatedly delayed by disputes over who is eligible to vote.

The BBC North Africa correspondent says both sides know that the total number of voters is the key to determining who wins.

Morocco wants to add 65,000 names to the voter list, but Polisario charges that these are Moroccans with no links to the territory and would swing the vote in Morocco's favour.

Mr Annan visited both neighbouring Morocco and Western Sahara earlier this month before interrupting his trip because of the crisis in Iraq.

UN losing patience

Mr Annan has already proposed that the referendum should be postponed by another year until December 1999.

However, he warned that if the deadlock continued the UN could pull out of what has proved to be an intractable and expensive peace-keeping operation with no end in sight.

After meeting Polisario leaders, Mr Annan flew to Algiers for talks with officials there.