The lives of more than a billion people are threatened by the spread of deserts, according to experts. The warning came at the opening of the United Nations conference on desertification in Bonn, which is being attended by Switzerland.

The director of the UN secretariat to combat desertification, Hama Arba Diallo, said a fifth of the world's population was at risk. He said land erosion and the spread of deserts was leading to growing poverty, a scarcity of food and increased migration.

Diallo said no time could be wasted in finding ways to combat the problem caused by climate change. He urged rich industrialised countries to step up financial help to the affected areas.

The World Health Organisation (WHO) warned that desertification was a major threat to human health, triggering epidemics and infections. It said women and children were particularly at risk.

Switzerland is one of 172 countries taking part in the two-week conference. It is represented by a delegation led by Henri-Philippe Cart, the deputy director of the Swiss Agency for Development and Cooperation.

The development agency has invested SFr94 million ($55 million) over the past three years in projects to combat the spread of deserts in Asia and Latin America.

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