"Anybody who leaves home abruptly and moves to the countryside will have all these needs. And the longer they stay,the more problems they have."

Alex earlier estimated the total number of people who had fled their homes in North Darfur at 50,000.

Rebel groups said last month government forces and allied militias launched a series of heavy ground and air assaults on their positions in northern Darfur.

International experts estimate that 200,000 people have died and more than 2.5 million people have fled their homes since the violence flared in Darfur in 2003, when mostly African rebels took up arms against the Arab-dominated central government.

Khartoum says 10,000 have died and accuses the international media of exaggerating the crisis.

Villages emptied

The Sudanese army said soldiers had entered some areas the rebels had mentioned, but that troops were only protecting roads against bandits.

Aid workers said at the time that entire villages had been emptied after residents took shelter in surrounding mountains and open land - cut off from food aid and clinics.

Alex and an international aid source said humanitarian access to the areas near Disa and Birmaza was very limited.

"Nobody is able to reach the area," said the aid worker, speaking on condition of anonymity.

"The security situation is unstable so trying to reach them is very dangerous."

Alex said food and water were not the only supplies needed.

"The season is changing. It is starting to get cold at night, so they need non-food items as well," he said.