CAIRO, Egypt - Malnutrition has increased among children in Darfur over the past year despite a massive humanitarian aid effort in the war-torn Sudanese region, according to a UN report obtained Thursday.

Four years since the conflict began, escalating violence against local people and aid workers alike have made it difficult to get food and other aid to the 4.2 million Darfurians affected, UN officials said.

The study, obtained by The Associated Press, found that 16.1 per cent of children affected by the conflict suffer from acute malnutrition, compared to 12.9 per cent a year earlier.

It was the first time that the rate has been above the World Health Organization's 15 per cent "emergency threshold" for malnutrition since 2004, a year after the conflict in Darfur began, when it ran at 21.8 per cent.

"We in the UN have been warning for some time that the nutritional situation in Darfur has been deteriorating," said Stephanie Bunker, "It is worrying. We are concerned because insecurity has compromised our ability to reach people in need. We've had violence against the people of Darfur and against aid workers."

She said 290,000 Darfurians were driven from their homes by violence in 2007.

The United Nations has been leading a US$1 billion-a-year aid effort in Darfur, with some 13,000 aid workers from the UN and other humanitarian agencies providing food and medical help for those affected by the conflict, including 2.5 million people driven out of their homes.

But attacks on humanitarian workers have increased 150 per cent this year amid the region's chaos, according to the UN At least 12 aid workers were killed, more than 100 kidnapped and 66 assaulted or raped, while over 60 aid convoys were ambushed and 100 vehicles hijacked. Some aid groups have reduced their staff because of the attacks, which are blamed on Darfur's numerous armed groups.

Bunker said the violence fluctuates across Darfur, making a particular area inaccessible to aid workers for one period, then open later, forcing humanitarian groups to sometimes drop food supplies by helicopter rather than having a constant presence on the ground.

Sudanese government officials had no immediate comment on the UN report, which was prepared by UNICEF, the Word Food Program and the UN's Food and Agriculture Organization.

The report was based on a survey of 30 clusters of 25 households each from around Darfur. Malnutrition was surveyed among children between 6 months and five years old, by measuring the weight-to-height ratio.

More than 200,000 people have been killed since the violence began in Darfur in 2003, pitting ethnic African rebels against the military of the Arab-led Khartoum government. Arab militias known as janjaweed, allied to the government, are accused of widespread atrocities against ethnic African civilians.

A force of some 7,000 African Union peacekeepers has been in Darfur since 2004, but has been too understaffed and underequipped to protect civilians and aid workers. A joint UN-AU force of 26,000 peacekeepers is due to deploy starting in January.