The U.N. Office for the Coordination of Humanitarian Affairs in a report published Wednesday said there are emerging reports of violence among members of different ethnic groups in Sudan.
"There is a growing sense of panic among some of the displaced populations who find themselves trapped by the ongoing violence and the ethnic fault lines," the report read.
Conflict in Sudan has centered on the de facto border region between Sudan and southern Sudan, which gains formal independence next month.
The U.S. State Department in a statement condemned the blockade of humanitarian flights by the government in Khartoum and complained that humanitarian facilities in the region were looted.
"We deplore these acts and call on the parties to immediately allow full and unfettered access for aid workers to provide much needed humanitarian assistance to tens of thousands of people displaced from their homes and made vulnerable by renewed conflict," the statement read.
U.S. Secretary of State Hillary Clinton was in the region this week and pressed both governments to end the violence. U.S. President Barack Obama called for calm, adding there was "no military solution" to the conflict in Sudan.
Southern Sudan gained the right to form an independent state as part of a comprehensive peace deal signed in 2005.
Both governments had discussed the situation during multilateral meetings in Ethiopia. British Foreign Secretary William Hague warned both sides not to squander the opportunity for peace.
"I strongly urge all parties to work together to seek an early peaceful solution," he said in a statement.
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