The United Nations is calling for increased aid from donors to avert a humanitarian catastrophe in Africa's drought-hit Sahel region.

John Holmes, the outgoing head of the UN Office for the Co-ordination of Humanitarian Affairs (OCHA) said more than $229m was still needed to respond to the crisis in Niger, the worst hit of the countries in the region.

About 7.1 million people, roughly 47 per cent of Niger's population, are facing food insecurity, Holmes said, citing an April survey.

UN officials also point out that last year's poor rains have resulted in a 30 per cent decline in cereal output in Niger compared with 2008, while production of food for livestock is 62 per cent below requirements.

Food prices also remain high, despite a decline from a peak in 2008.

More than 300,000 children under the age of five are said to be at risk of acute malnutrition in Niger, including 20 per cent who will suffer medical complications, OCHA said.

Rising malnutrition

Global malnutrition levels have also significantly increased, with a June survey showing an acute malnutrition prevalence exceeding 15 per cent, up from 12.3 per cent last year.

In neighboring Chad, Holmes said donors had so far only pledged 45 per cent of the $542m requested and that 1.6 million people face food insecurity and malnutrition.

Another 600,000 people in Mali and 300,000 in Mauritania are similarly at risk.

Donors have so far either committed or delivered more than $142m to the region.

Holmes, who visited Niger in April, said that UN agencies and non-governmental organisations were present on the ground and better prepared to respond than during a similar crisis five years ago.

'Alarming situation'

"What we need to do is step up that capacity even further and make sure it is resourced because people have no food or where there's food, they need money to buy it," he said.

Aid agency Oxfam echoed a similar plea, saying the food crisis was reaching disastrous levels.

"The eyes of the world have trouble seeing this crisis," the group's deputy regional director Raphael Sindaye told reporters last week.

"The already extremely alarming situation is clearly going to become disastrous," Gilles Marion, Oxfam's director in Mali, added.