The U.N. High Commissioner for Refugees (search) said Thursday an unprecedented attack on a displaced persons' camp in Sudan (search)'s embattled Darfur region reportedly has killed 29 people.

Antonio Guterres, chief of the U.N. agency, cited aid workers' reports of the attack Wednesday at Aro Sharow camp, which also left 10 seriously injured. These reports said up to 300 armed Arab men on horses and camels attacked the camp in northwest Darfur (search) and burned about 80 makeshift shelters.

Between 4,000-5,000 Sudanese were believed to be living in the camp and most reportedly fled into surrounding countryside, UNHCR said. The nearby village of Gosmeina was also reportedly attacked and burned.

"The government of Sudan has a responsibility to ensure security for all of its citizens," Guterres said.

"As long as this insecurity continues, the international community cannot provide the assistance that is so desperately needed by hundreds of thousands of people."

Residents stayed in the Aro Sharow camp at night for safety, but would return to their nearby villages during the day to cultivate their fields, the agency said.

U.N. humanitarian chief Jan Egeland warned that escalating violence in Darfur is threatening aid for millions of people as increasing numbers of international staff come under attack.

"It could all end tomorrow," he said. "It's as serious as that.".

UNHCR said it was also concerned that the deterioration in security is slowing aid supplies and could prompt Darfur's displaced people to flee again — possibly to neighboring Chad, which already has more than 200,000 Sudan refugees.

The Darfur crisis began when rebels took up arms against what they saw as years of state neglect and discrimination against Sudanese of African origin. The government is accused of responding with a counterinsurgency campaign in which the ethnic Arab militia, known as Janjaweed, committed widespread abuses against ethnic Africans.

At least 180,000 people have died in the Darfur conflict — many from hunger and disease.