Sudanese children collect water from a well in the village of Brikatouly in South Darfur, Sudan

The top United Nations humanitarian coordinator in Sudan says that fighting among rebel factions is blocking humanitarian access to the war-torn Darfur region. The U.N. also expressed concern about recent government restrictions in eastern Sudan, which have prevented aid from reaching vulnerable people there.

Humanitarian access in Darfur has been severely hindered by fighting among rebel factions in the region, top U.N. humanitarian coordinator Manuel Aranda da Silva said on Monday.

Since the May 5 signing of the Darfur Peace Agreement, attacks by Sudan government forces have decreased, Aranda said, while rebel fighting is now the main cause of concern in the region.

"We have had a deterioration of access in Darfur. We have at least 250,000 people that we cannot reach. Many due to in-fighting or deterioration of security in specific areas. We are trying to deal with it by negotiating with the different parties involved," said da Silva. "Not very positive progress in northwestern Darfur. Most of the U.N. agencies and NGO's have been obliged to pull out from that region."

Critics have charged that the Darfur Peace Agreement was doomed from the beginning.

Only one faction of the rebel Sudan Liberation Army signed onto the deal, along with the Sudan government.

Another SLA faction, led by Abdel Wahid Mohamed Nur, and the rebel Justice and Equality Movement refused to sign onto the agreement.

Nur's faction and Minnawi's are now fighting one another, leading to increasing instability in Darfur.

Da Silva added that he is equally concerned over an aid blockade in volatile Eastern Sudan. The U.N. has been refused access to the region by the Sudan government in recent days.

"When it comes to the east, I am very disappointed," he said. "Since the beginning of last week, we have been denied access to visit refugee camps. And if we cannot access, then we cannot provide assistance. This is a very strange development. If it is not solved very soon, we are going to have enormous problems in these refugee camps in the east."

Eastern rebels have complained that Sudanese oil revenue has not benefited the impoverished region.

Peace talks between the Sudan government and rebels are under way in the Eritrean capital of Asmara.

The three-year-old Darfur conflict began when rebels rose against the Khartoum government, complaining the remote region remained undeveloped due to neglect.

Sudan is charged with arming militias to crush the rebellion, resulting in a savage campaign of rape and murder in which tens-of-thousands have died and some two million more have been displaced.