LONDON -- A third of children in the developing world, 150 million in total, suffer malnutrition, a report released on Wednesday said.

The UN Children's Fund, UNICEF, said the figures, the first for a decade and compiled from the largest-ever data collection on infant well-being, revealed that while "spectacular gains" had been made against some nutritional deficiencies, malnutrition was still a major problem.

"The familiar symbol of the visibly starving child misrepresents the problem. In reality, most malnutrition is totally invisible," said the report, entitled "Malnutrition: The News".

The survey, conducted in more than 100 countries, found that child malnutrition in the developing world had fallen from 32 percent to 28 percent.

Almost half of children in south Asia were malnourished compared to fewer than a third in sub-Saharan Africa, the report said.

But the report did present some good news, with 18 countries reducing child malnutrition by 25 percent or more, including populous nations such as China, Mexico, Indonesia, Bangladesh and Vietnam.

It was the frequency of illness rather than a lack of food that was the major problem, the report said, with the overwhelming majority of malnourished children living in homes with enough food.

Illness caused a loss of appetite, used up calories fighting infections and drained away vital nutrients in vomiting and diarrhea.

The vast majority of affected children become malnourished in the first three years of life -- a critical period for brain and body growth.

"The greatest tragedy of malnutrition is that it prevents children reaching their full potential," Reuters quoted former James Bond actor Roger Moore, a UNICEF goodwill ambassador as saying.

On the positive side, more than 70 percent of the developing world's households now use iodized salt -- a rise of 50 percent --- protecting an estimated 12 million children a year from suffering brain damage as a result of iodine deficiency.

Vitamin A supplements now reached half the world's children, saving a third of a million lives a year, and the decline in breast-feeding -- key to good nutrition -- appeared to have ended, the report said.