Search for Darfur aid workers

Darfur has been described as the world's worst humanitarian crisis

United Nations security officers are hunting for eight aid workers missing in a rebel-controlled area of Darfur.

The eight were working for the Red Crescent and World Food Programme when they disappeared on Saturday.

The Sudanese government says they were kidnapped by rebels of the Sudan Liberation Army; something aid officials say they cannot confirm.

UN officials are set to issue findings on efforts to stop attacks that have exacerbated a humanitarian crisis.

The UN Security Council will meet on Thursday to discuss whether to take action against the Sudanese government.

The UN had threatened measures if, by 30 August, the security situation in the western region of Darfur had not improved and the militias, blamed for killing civilians, had not been reined in.

DARFUR CONFLICT More than 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: Has security improved? Eyewitness: Life in north Darfur

Meanwhile 22 Sudanese aid workers kidnapped in Darfur have been released.

Working on a Unicef vaccination programme, the ministry of health workers were abducted by Justice and Equality Movement rebels on Saturday.

They were released in the southern town of Nyala on Tuesday, Unicef says.

Secretary-General Kofi Annan is expected to decide on Tuesday whether the Sudanese government is complying with UN demands.

More than one million black Africans in Darfur have been driven from their homes, primarily by the pro-government Arab Janjaweed militia.

Sudan's government denies being in control of the Janjaweed and President Omar al-Bashir has called them "thieves and gangsters".

The BBC's Hilary Andersson in southern Darfur says large parts of the region remain insecure for displaced civilians.

It was in southern Darfur that the aid workers were last seen. Three of them are from UN's World Food Programme and five of them from the Sudanese Red Crescent.

The African Union and a UN official say attacks on civilians are continuing. AU chairman President Olusegun Obasanjo of Nigeria said reports of such attacks had been verified by AU ceasefire monitors and he has written to President Bashir asking him to ensure the attacks cease.

The UN's Dennis McNamara in Kenya said he too had evidence of widespread attacks, including multiple rapes and harassment of civilians by pro-government militias.

Troops sent

The UN's special envoy to Sudan, Jan Pronk, is expected to address the Security Council on Thursday about what progress has been made in returning stability to Darfur since the UN passed the resolution on 30 July.

The Council will then debate the issue after hearing a report by Mr Annan.

HAVE YOUR SAY The world community has a duty to alleviate the abject suffering of the displaced people in Darfur Pancha Chandra, Belgium Send your views

The BBC's Stephen Gibbs at the UN in New York says it seems likely that the UN will conclude that Sudan has gone some way - but not far enough - to alleviate this crisis.

The threat of sanctions appears to be dimming, he adds.

The Sudanese Foreign Minister Mustafa Osman Ismail said he hoped the Security Council would come to a "reasonable decision".

"We wish the relationship between Sudan and the Security Council will not be in the way of confrontation," he told Associated Press television in an interview.

Nigeria has sent about 150 troops to Darfur to guard ceasefire monitors, as peace talks continue in Abuja.

They will work alongside 150 Rwandan troops sent to the region earlier this month as part of an African Union protection force.