GENEVA -- The soaring food prices lead not only to empty stomachs but also empty classrooms in poor countries as parents send their children to work rather than school, UNICEF warned on Tuesday.

The higher prices are making families "reduce their budget, to cut down on education and to remove their children from school to make them work" said Veronique Taveau, spokeswoman for the UN children's agency.

She added that the organisation was "extremely concerned" by the price increases.

The impact of higher food prices is particularly marked in poor countries where 75 percent of a family's revenues go on food, compared to rich countries where just 15 percent of a household's income is spent on meals.

A drop in school attendance is already being observed in Nepal, said World Food Programme spokeswoman Christiane Berthiaume.

The country is particularly vulnerable as it depends on food imports from China and India, which are restricting exports, said Berthiaume.

In many countries, the only warm meal children get in a day is the meal served in school canteens, she added.

In Cambodia, the WFP was also forced to suspend its food distribution to school canteens as its local suppliers decided to drop their contracts with the group.

"They prefer to sell elsewhere at a higher price," said Berthiaume.

The WFP distributes 450,000 meals a day in Cambodian school canteens at 25 cents per week per child.

Food security has become a major concern in recent weeks as supplies of basic commodities have dwindled in the face of soaring demand, triggering riots and outbreaks of violence from Haiti to Indonesia.

The World Bank on Sunday said a doubling of food prices over the past three years could push 100 million people in developing countries further into poverty. It urged developed nations to step up and tackle the issue.