The United Nations has issued an urgent appeal for aid to Africa, saying the continent faces an irrevocable crisis without it.

The head of UN Humanitarian Affairs, Sergio Viera de Mello, said less than half the money needed had been received this year and appealed to donor countries to provide an extra $444m.

The UN says the shortfall in aid to Africa is now so severe that the plight of victims of war and natural disasters is reaching crisis proportions.

A total of $800m is needed to tackle the problems of famine and disease, as well as to bolster efforts to end war in several countries.

Because of the lack of money, aid programmes have been cut back and life-saving assistance often has to be denied.

In Somalia, for example, more funds are needed to help at least a million people who are threatened with famine.

In Angola, two million people are affected by the intensifying conflict and there are insufficient supplies to help them.

'Donors can afford it'

Mr de Mello said the crisis comes at a time when donor countries can well afford to give more aid.

"This decline has occurred against the background, in most of the donor countries, of positive growth rates," he said.

He pointed to the booming stock markets in developed countries, with the markets in New York and Europe increasing by 70% over the past three years, and in some cases unprecedented budget surpluses.