Almost 500 families lost their homes in one part of Kassala state, while more than 500 others are believed to have escaped the flooding and sought safety at a camp known as Kilo 26, in the state's Khashm El Girba district, said Felix Ross, of the office of the UN High Commissioner for Refugees.

"Families have been out in the open for several days," he told AFP.

Flood waters prevented the UNHCR from accessing two other villages, Arab 1 and Arab 2 in Khashm El Girba, where a smaller number of people are believed to have been affected, he said.

Flooding was first reported more than a week ago, Ross said.

UN agencies have been assisting the government by providing tents, mosquito nets, plastic sheeting, blankets and kitchen sets, he added.

"It's a real disaster," said Khashm El Girba district chief Yahya Mohammed Ahmed.

Thousands of people have lost their homes and access to drinking water, or are cut off by the flood waters, he told AFP, adding that no deaths had been reported so far.

"We expect more rain and more water in the coming days, which will worsen the situation," he said.

In May, Khartoum ordered seven international aid organisations to cease operations in eastern Sudan, saying some projects were badly managed, of poor quality and too costly.

The agencies provided healthcare for women and children, demining, water, sanitation and nutrition projects for about 600,000 people, aid agencies said.

A 2006 peace deal ended more than a decade of low-level insurgency in Sudan's east but tensions remain.

Flooding has also affected at least 14,000 people in the Darfur region of western Sudan over the past week, the UN's humanitarian agency said.