ROME — Nearly 200 million children in poor countries have stunted growth because of insufficient nutrition, according to a new report published by UNICEF Wednesday before a three-day international summit on the problem of world hunger.

The head of a U.N. food agency called on the world to join him in a day of fasting ahead of the summit to highlight the plight of 1 billion hungry people.

Jacques Diouf, director-general of the Food and Agriculture Organization, said he hoped the fast would encourage action by world leaders who will take part in the meeting at his agency's headquarters starting Monday.

The U.N. Children's Fund published a report saying that nearly 200 million children under five in poor countries were stunted by a lack of nutrients in their food.

More than 90 percent of those children live in Africa and Asia, and more than a third of all deaths in that age group are linked to undernutrition, according to UNICEF.

While progress has been made in Asia — rates of stunted growth dropped from 44 percent in 1990 to 30 percent last year — there has been little success in Africa. There, the rate of stunted growth was about 38 percent in 1990. Last year, the rate was about 34 percent.

South Asia is a particular hotspot for the problem, with just Afghanistan, Nepal, India, Bangladesh and Pakistan accounting for 83 million hungry children under five.

"Unless attention is paid to addressing the causes of child and maternal undernutrition today, the costs will be considerably higher tomorrow," said UNICEF executive director Ann M. Veneman in a statement.

Diouf said he would begin a 24-hour fast on Saturday morning. The agency also launched an online petition against world hunger through a Web page featuring a video with Diouf counting from one to six to remind visitors that every six seconds a child dies from hunger.

The U.N. children's agency called for more strategies like vitamin A supplementation and breast-feeding to be rolled out more widely. That could cut the death rate in kids by up to 15 percent, UNICEF said.

Not everyone agreed.

"It is unrealistic to believe malnutrition can be addressed by any topdown U.N. scheme," said Philip Stevens, of International Policy Network, a London-based think tank. "The progress UNICEF's report points to in improving nutrition is almost certainly a result of economic growth, not U.N. strategies."

The Rome-based FAO announced earlier this year that hunger now affects a record 1.02 billion globally, or one in six people, with the financial meltdown, high food prices, drought and war blamed.

The agency hopes its World Summit on Food Security, with Pope Benedict XVI and some 60 heads of state so far expected to attend, will endorse a new strategy to combat hunger, focusing on increased investment in agricultural development for poor countries.