Armed men seized two foreign civilians working for Darfur's peacekeeping force on Saturday, the fourth kidnapping in the remote Sudanese region since March.
"They were abducted by armed men from their residence in Zalingei. The incident took place in the early hours of this morning," Unamid spokesman Noureddine Mezni told Reuters.
It was the first time international staff from the joint United Nations/African Union force had been abducted, he said.
Mr Mezni declined to give the names or nationalities of the man and woman who were kidnapped as their families had not yet been informed.
The kidnappers made contact with the peacekeepers soon after the abduction. "They told us of their willingness to talk to Unamid," Mr Mezni said, without giving details of their demands.
The kidnapping, in Zalingei in the western part of Darfur, happened two days after the departing commander of the force, Martin Luther Agwai, told reporters that Darfur suffered from banditry but was no longer in a state of war.
Aid workers say they have experienced increased hostility in the region since the International Criminal Court issued an arrest warrant for Sudan's president Omar Hassan al-Bashir on war crimes charges.
Khartoum ordered out 13 foreign groups and shut down three local ones after the ICC issued its warrant in March, accusing them of passing information to the court, which they deny.
Two women from Irish charity Goal remain in captivity after being snatched in early July. Another aid worker is missing after a raid just over Darfur's border in neighbouring Chad earlier this month.
Sharon Commins (32), from Clontarf, Dublin, and her Ugandan colleague Hilda Kawuki (42) were taken from a Goal compound in north Darfur on July 3rd.
Zalingei, around 100 kms (62 miles) from the Chadian border, is the birthplace of some of Darfur's best-known rebels, including Sudan Liberation Army founder Abdel Wahed Mohamed Ahmed al-Nur, and is a hotbed of anti-government sentiment.
Mr Al-Nur, who is now based in Paris, denied that any of his rebel fighters were responsible for the kidnap, and pointed the finger at government-allied militias.
"This is not our behaviour. We are a responsible movement. We fight against terrorists and this kidnapping is a terrorist act," he said.
"This is the continuation of the government's campaign to terrorise people on the ground. They want to complicate the mission of anyone helping the people of Darfur."
Representatives of Sudan's government were not immediately available for comment.
Al-Nur said the kidnap showed the weakness of Unamid's mandate.
"Unamid's first job is to protect civilians but they are not able to protect themselves because of the mandate. We need a mandate for peacemakers, not peacekeepers."
Reuters