"No emergency assistance has gotten to these people," said Alex. "For the last five or six weeks, they have been living off assistance they are getting from other people ... or what they can scrounge for."
Most of the newly displaced are living in the desert rather than in refugee camps, said Alex. Many of them had been displaced by fighting before but had returned ahead of the recent attacks, he added.
More than 2.5 million people have been displaced in Darfur and up to 300,000 killed since ethnic African groups rebelled against the Arab-dominated national government early in 2003.
A recent round of fighting began in August when government troops attacked rebel-held areas along the border with Libya in northern Darfur - sometimes accompanied by aircraft and Arab militias.
In September, the fighting moved south toward more populated areas. But the U.N. and aid workers said they have had little access to the areas because of the continued tension.
Some villages in the Jebel Marrah area in central Darfur were totally emptied by the September fighting, said an international aid worker, speaking on condition of anonymity for fear of government harassment.
The locals in the area were warned ahead of the fighting and about 10,000 of them fled before it broke out, said the aid worker.
Some of the villagers have begun to return to their farms for the harvest season, he added.
Government officials have said the recent offensive in August and September was targeted at bandits that had increased attacks against U.N. agencies and aid convoys.
But rebel groups have said the government was trying to clear them out of strategic areas to change the balance of power on the ground ahead of peace negotiations.
Sudanese President Omar al-Bashir recently launched a new peace initiative at a conference attended by international supporters.
But the rebels boycotted the meeting, saying it was a sham intended to rally support for the president, who is facing charges of genocide in Darfur by the International Criminal Court.