Four peacekeepers are missing in Sudan's troubled Darfur region after a flash flood hit while they escorted an aid mission, UNAMID said on Monday.

"A UNAMID rescue team from El Geneina, West Darfur, found two peacekeepers alive while a search is ongoing to locate the other four," an official of the African Union-United Nations Mission (UNAMID) told AFP.

UNAMID did not release the nationality of the troops involved.

The six were swept away "by a powerful current" while escorting the World Food Programme (WFP) to Misterei, about 50 kilometres (30 miles) southwest of El Geneina, the West Darfur state capital near Chad, the official said requesting anonymity.

"The incident occurred while the peacekeepers attempted to pull out their truck which was stuck in the mud of a river valley", the official added.

Floods across Sudan this month have killed about 50 people and affected more than 500,000, according to government figures.

WFP spokeswoman Amor Almagro told AFP that the agency's five Sudanese and two foreign staffers are all safe.

They were going to monitor WFP projects in Misterei, where the organisation gives food assistance to about 10,900 people, she said.

In August last year three UNAMID peacekeepers from Tanzania drowned after their armoured vehicle became stranded while crossing a swollen river, UN Secretary General Ban Ki-moon reported to the Security Council last year.

He has also raised concerns about equipment shortfalls "which mainly pertain to the serviceability of armoured personnel carriers," and adversely affect the mission's operations.

UNAMID is one of the world's largest peacekeeping missions, with about 20,000 troops and police.

Its mandate is to protect civilians and provide security for aid workers in the region where violence has worsened this year, mainly because of inter-Arab tribal battles.

Thirteen peacekeepers have died in hostile action in Darfur since last October.

More than one million displaced people have been living in Darfur camps for a decade, the UN says, since rebels began an insurrection against the Arab-dominated government.