At least 69 children have died from malnutrition and sickness after floods washed away crops in isolated villages in southeast Sudan in recent weeks, U.N. agencies said on Thursday.

Blocked roads and a lack of air transport are preventing the supply of emergency rations to parts of the region, the agencies added.

Aid workers fear for villagers in the Kurmuk region of Blue Nile state, where thousands of former refugees have returned home in the past few months after years of exile across the border in Ethiopia. Some remote villages unreachable by aid workers are at increased risk, the agencies said.

The U.N.'s refugee agency said villagers in the region had used up six months of emergency food given to them when they arrived in Bellila and nearby villages earlier this year.

"There is now a food crisis," an agency spokeswoman said. "The harvest was bad and food prices in the market are very high. The seeds that were in the field have also been washed away by floods."

The U.N.'s World Food Programme said it has a month's worth of emergency food for the region, but floods had blocked roads and it has not yet obtained air transport to supply the aid.

Villagers who fled more than two decades of north-south civil war in Sudan have been slowly returning to the area after a 2005 peace deal, but three years on and the region has seen little development.

A report from the U.N.'s mission in Sudan, seen by Reuters, said the World Health Organisation sent a team to Bellila this month to set up a health clinic and to assess the situation.

"The findings were alarming. The returnee community had finished their six-month food ration some months ago and did not have sufficient food ever since," the U.N. report said.

The report said 48 children died in the village of Gindi and another 21 in Borfa in August and September, all of them aged one to six. They died from malnutrition, diarrhoea and malaria.

Almost half of the 1,200 villagers needed medical treatment, a situation likely to be similar in other remote areas of Kurmuk, the report said.

Sudan, in the midst of its annual rainy season, has been hit by a series of floods in recent weeks, but the U.N.'s refugee agency said the needs were particularly acute in Blue Nile because of the remoteness of the villagers.

Villagers were also in a particularly vulnerable condition having just returned after years in refugee camps, it added.