UNITED NATIONS (Reuters) -- Rising violence in Sudan's Darfur region has killed more aid workers in July than over the previous two years, seriously jeopardizing relief assistance, UN humanitarian officials said on Monday.

Eight aid workers died last month as fighting among Sudanese factions increased. Concern for aid worker safety has forced humanitarian groups to reduce their presence in Darfur homeless camps to its lowest level since the civil war escalated in 2003, UN officials said.

In addition to the deaths, aid workers have recorded an increase in hijackings, lootings and attempted ambushes of vehicles carrying food and health supplies, according to the UN Office for the Coordination of Humanitarian Affairs.

Many of the attacks happened while workers were helping suffering populations, said Manuel da Silva, the UN deputy special representative in Sudan. "The level of violence being faced by humanitarian workers in Darfur is unprecedented," da Silva said.

"If this situation continues, we risk losing all that we have gained over the past year."

Tens of thousands of people have died in the violence that escalated in early 2003 when mostly non-Arab rebels, complaining of neglect, rose up against the Arab-dominated Khartoum government. Sudan retaliated by arming mainly Arab militia, known as Janjaweed, who began a campaign of plunder and murder against non-Arab tribes.

More than 2 million people have been thrown out of their homes, many living in squalid camps. Now rebel factions are fighting each other with camp residents taking sides.

"The situation is made even more serious by the fact that the need for humanitarian assistance is increasing while our ability to respond is being ever more restricted," da Silva said.