David Willey in Rome details the UN's assessment on urban expansion

In its annual report, the FAO says the number of chronically hungry people in the world is continuing to rise.

The infrastructure needed for feeding massive populations - involving co-ordination between producers, transporters and sellers - is not keeping up with urban expansion.

By the millennium there will be 20 cities of more than 10m people, nearly all of them in the third world.

The number of impoverished city dwellers will have risen from 400m in 1990 to 1bn, and there will be an "anarchic spread" of shanty towns, sickness, corruption and inflation.

Optimistic aims

At the FAO world food summit in Rome two years ago, agriculture ministers said they aimed to halve the number of people going hungry by the year 2015.

These latest statistics show the trend is already in the opposite direction.

Some children begin life suffering from malnutrition

Population growth continues unabated in the world's biggest cities, meaning more shanty towns, more overcrowding and more middle-men in food distribution.

Soon, the world's urban population will exceed the number of people living in rural areas.

Inadequate support

The FAO also warned that poor city infrastructure is linked to the costs of food.

Poor people spend up to 80% of income just on food, much more than rural families.

Street markets are the main places for buying food

City people also often have a worse diet.

Wholesale food markets are also often badly sited, costly and unfit for their purpose, the FAO said.

In Africa, they lack basic equipment, such as refrigeration, and in Latin America, markets pollute the environment with their waste and block city centres with delivery trucks.

The FAO stressed the important role played by small markets and street vendors who provide food for the poorest people.