The UN official added that there was an increase in the cases of malnutrition as well as a severe lack of transportation means to carry food supplies to the war-torn Darfur.
He also warned that more obstacles in delivering relief would appear with the approach of the rainy season.
The UN official called for more financial aid in order to overcome the difficulties.
In addition, Fill said the refugee camps in Darfur need more security protection.
He said there were reports of lootings of livestock and vehicles in West Darfur state and humanitarian workers in South Darfur state received threats.
Sudan's arid and impoverished western region of Darfur has been in the grip of conflicts for more than two years since rebels took up arms against the government, accusing it of neglect. Many people have been killed and more displaced.
The Sudanese government and the Darfur rebels are currently holding talks toward a peaceful settlement in Nigerian capital Abuja under the auspices of the African Union.