STORY: Fierce fighting, rampant looting and reams of red tape are hampering Sudan's relief effort, aid workers say.
More than half the population, or about 25 million people, now need help, the U.N. says, up from 16 million before the conflict broke out in April.
At least 1.2 million people have been internally displaced.
Jean-Nicolas Armstrong Dangelser, emergency coordinator for medical aid group MSF, says millions of people in need are out of reach.
"Often we cannot move because the warehouse is being looted or because it's unsafe for our staff to move or because for the transporter it's unsafe to go. There is a lot of problems at the various checkpoints where the trucks are being held sometimes with the drivers being detained or so from time to time and sometimes with the aid not reaching the final place."
At least eight aid workers are among the hundreds of people killed in nearly seven weeks of fighting.
While the World Food Programme says food for 4.4 million people is at risk after an attack on its warehouses in El Obeid, a city southwest of Khartoum.
It says during the conflict, it has lost supplies in Sudan worth $60 million.
An official from the U.N.'s OCHA humanitarian agency said more than 160 vehicles have been stolen from aid organizations and scores of offices and warehouses have been looted.
Alyona Synenko is a spokesperson for the International Committee of the Red Cross.
"There is just the general state of lawlessness, the lootings have been widespread and just like the general criminality and that of course adds a different layer and makes it an extremely volatile and difficult environment to be working in.”
Aid workers say communications have broken down.
Securing visas to Sudan or travel permits to deliver relief inside the country has been a struggle, they say.
An army official said the foreign ministry was handling those visas and the ministry didn't respond to requests for comment.
MSF said it had teams stranded for more than two weeks in Port Sudan without being allowed to move to other states.
The head of the military authority there said there were no obstacles to delivering aid, but security procedures were causing small delays.