Insecurity in Myanmar's Rakhine State affects delivery of aidListen /
An ongoing curfew and the scaling down of humanitarian staff are also disrupting services.
The Office for the Coordination of Humanitarian Affairs (OCHA) said that UN agencies and humanitarian partners on the ground were seriously concerned about the situation.
Rakhine state has been the scene of waves of violence between Buddhists and Rohingya Muslims, which has seen hundreds of people killed and tens of thousands more made homeless.
Demonstrations in Sittwe last week caused damage to UN and international non-governmental organizations offices.
Despite the challenges, aid workers remaining in Sittwe have continued to provide assistance including food, water and healthcare.
In the wake of these attacks, Secretary-General Ban Ki-moon spoke on the phone to Myanmar President Thein Sein and urged him to ensure the safety of all staff members and their property.
The UN is closely consulting with the Government and local authorities to ensure that the conditions for the return of humanitarian workers are safe and secure.
Jocelyne Sambira, United Nations.