"We are troubled by the acute humanitarian emergency in the Sahel region where hunger threatens the lives of 19 million people and the stability of the region," said a statement from the organisations' joint development committee.

"Food security and food price volatility remain persistent threats to development and merit continued attention."

The IMF and World Bank, which are holding annual meetings in Tokyo, called for accelerated efforts to help millions in the vast desert area "permanently escape the cycle of emergency aid".

The Sahel stretches across a swathe of west Africa, including Burkina Faso, Cameroon, Chad, Gambia, Mali, Mauritania, Niger, Nigeria and Senegal.

The warning came amid preparations for an international military intervention aimed at reconquering northern Mali, home to the fabled city of Timbuktu, which was seized by Islamist rebels earlier this year.

In March, a military coup in the capital Bamako toppled President Amadou Toumani Toure, with the vast country's north and east falling to Tuareg rebels and militias linked to Al-Qaeda.

This year, more than 18 million people in the region have been hit by a severe food crisis, with some 1.1 million children facing acute malnutrition, according to the UN Office for the Coordination of Humanitarian Affairs.

The instability in northern Mali has led 400,000 people to leave their homes, with more than half fleeing into neighbouring countries, straining the infrastructure of already poor western African nations.