The situation deteriorates in Darfur, Sudan, as nearly half a million people have less access to humanitarian assistance following the increase of military activity, banditry and direct violence against aid workers in early December.
The insecurity has led to 250 humanitarian staff - from key locations across Darfur serving some 480,000 people- being temporarily evacuated.
At a time when humanitarian needs are rising fast, aid workers are facing unprecedented difficulties, said a group of leading international aid agencies working in the conflict-stricken region.
Already more than a third of Darfur is effectively out of bounds to aid agencies. Evacuations and new violence in December mean access levels are now even lower. A ceasefire is desperately needed to allow aid workers reach those in need, says Concern Worldwide Regional Director Angela O'Neill.
Concern Worldwide, in association with other agencies including World Vision, International Rescue Committee (IRC), Norwegian Refugee Council, and Oxfam International Goal, say: "All parties must urgently agree - and maintain - a ceasefire with immediate effect. They must ensure that aid workers are able to reach people in need."
With access to people in need already at its lowest point since mid-2004, five major areas suffered significant withdrawals of staff in the first week of December alone: El Fasher and Kutum in North Darfur; El Daein and Shearia in South Darfur; and Kulbus in West Darfur.
Although hopefully temporary, such evacuations are becoming more and more frequent, restricting the massive humanitarian response in a region where nearly four million people are now dependent on aid agencies for essential services such as food, water and healthcare.
Humanitarian agencies in eastern Chad are also finding it increasingly difficult to operate.