South Africa has told the United Nations it is withdrawing its troops from the joint UN-African Union mission in Sudan's strife-torn Darfur, a UN official said.
"The government of South Africa decided to withdraw its troops from the mission," said the official, who spoke on condition of anonymity.
The 850 troops will end operations on April 15.
"Of course, we will have to look at the contingency in terms of how we fill those gaps," she said.
Relations between Sudan and the United Nations have been tense over Khartoum's demands that the 17,000-strong UNAMID peacekeeping mission shut down.
South Africa's decision to pull out comes after five weeks of intense fighting that have sent some 85,000 people fleeing in the Jebel Marra area while UN officials are seeking to verify reports of an additional 50,000 on the move.
"It's a very large number for a very short period of time," said the official.
The 85,000 civilians, mostly women and children, have fled to north Darfur, but UN officials are seeking access to central Darfur where unconfirmed reports suggest 50,000 people have been driven from their homes there.
The Khartoum government has denied access to UNAMID, said the official.
A large influx of 63,000 civilians taking refuge at the UNAMID camp set up at Sortoni, in north Darfur, is prompting concerns.
"We are very concerned by the swelling of the makeshift camp at Sortoni. 63,000 people is a large number of civilians," said the official.
"We are very concerned on how in the mid-term we can deal with this."
Sudan's army has been trying to crush rebels of Abdulwahid Nur's faction of the Sudan Liberation Army (SLA-AW) in Jebel Marra, saying it was responding to attacks by the rebels.
The UN says that some 300,000 people have been killed in the fighting in Darfur since 2003 and 2.5 million displaced.
