MADRID, August 28, 2008 (AFP) - The United Nations has not renewed the mandate of its mediator on the Western Sahara dispute, Peter van Walsum, the Dutch diplomat announced in an article in a Spanish newspaper Thursday.

The Polisario Front, which is seeking independence for Western Sahara, announced last month it was ready to pursue direct negotiations with Morocco over the region but wanted Van Walsum replaced.

It charged the 74-year-old diplomat 'is biased in favour of Morocco after a declaration that the independence of Western Sahara is an unrealistic option.'

Van Walsum, who has been in the post since 2005, said UN Secretary General Ban Ki-moon has not renewed his mandate, which expired on August 21.

'I am writing this tribune as former personal envoy of the Secretary-General of the United Nations for Western Sahara,' Van Walsum said in an op-ed piece for the newspaper El Pais.

'I was originally appointed to this post by Secretary-General (Kofi) Annan in August 2005, and the fifth semi-annual extension of my appointment expired on August 21th last.'

In an interview with El Pais earlier this month, Van Walsum said the Polisario Front's demand for independence is not achievable even though it is backed by international law.

The Polisario has 'international law on its side,' he said in the interview published on August 8. 'But the Security Council is not ready to exercise its authority ... and impose it.'

Western Sahara is a former Spanish colony which was annexed in 1975 by Morocco. The Polisario Front, backed by Algeria, wants independence for the territory on the west African coast.

The two sides agreed to a truce in 1991 under the auspices of the United Nations.

Talks in the New York state town of Manhasset have been going on since June 2007. The fourth round of talks ended last March without success, and a date for a fifth round has not been set.

Rabat has offered a form of autonomy for the territory under Moroccan sovereignty, while the Polisario wants a referendum on self-determination.