Aid organisations say the refugees do not have adequate supplies

Hundreds of thousands of displaced people are sheltering in the camps.

UN official Anne Wood told the BBC that there had been an increase in malaria, diarrhoea and respiratory infections.

Meanwhile the African Union announced on Saturday that Sudan's government would hold peace talks with two rebel groups in the Nigerian capital Abuja.

African Union spokesman Adam Thiam said representatives of both sides had agreed to start the talks on 23 August.

An earlier effort to persuade both sides to attend peace talks failed when rebels from the Sudan Liberation Movement and the Justice and Equality Movement said they would not participate until Sudan demilitarised Darfur and prosecuted Arab militia there.

Officials from the UN, Arab League and African Union will also discuss the crisis in a series of meetings on Sunday.

It is believed the talks, which coincide with an emergency meeting of Arab foreign ministers in Cairo, will cover the possibility of deploying Arab observers in Darfur to assist those of the African Union.

'Not secure'

Ms Wood, who heads the UN office for the coordination of humanitarian affairs in Geneva, said the UN was still in the process of trying to avert the crisis.

DARFUR CONFLICT 1m displaced Up to 50,000 killed More at risk from disease and starvation Arab militias accused of ethnic cleansing Sudan blames rebels for starting conflict Q&A: Darfur conflict Text: UN Darfur agreement More refugees get food aid Sudan media rallies public

She added the message they were consistently hearing from the displaced population was that they did not feel secure and would not go back to their villages.

This has meant that they are totally dependent on food handouts.

In addition to food, the internally displaced people are given a water container, plastic sheets and a blanket each.

With the heavy rains every night, these items hardly provide adequate shelter.

Aid workers fear the displaced camps are likely to become breeding grounds for many illnesses with their woefully poor sanitation.

The WHO has said that almost 150 cases of hepatitis-E have been confirmed in the region.

Earlier on Saturday, a UN investigator on executions blamed Sudan's government for extra-judicial killings in the western region of Darfur, which she said amounted to crimes against humanity.

Asma Jahangir added that "millions of civilians" caught up in the crisis were at risk.

Khartoum has denied supporting the Janjaweed rebels which is blamed for much of the violence.

For several weeks, it has been trying to absorb Janjaweed elements into the paramilitary Popular Defence Force, and into its police force.

The report says the Sudanese government appears oblivious to the humanitarian crisis in Darfur and described the persistent denial of the disaster by most government officials as "shocking".