Hundreds of millions of children and adults in Asia's rapidly expanding cities are undernourished, and will remain so without "inclusive, sustainable and nutrition-sensitive" urban planning, United Nations officials said Friday.

The Asia-Pacific region has the world's highest rate of urbanization and is home to more than half the world's 821 million undernourished people, four U.N. agencies said in a report released in Bangkok.

"Progress in reducing undernourishment has slowed tremendously," said the regional heads of Food and Agriculture Organization, the U.N. Children's Fund, the World Food Program and the World Health Organization.