"Two police advisers...got abducted about 100 meters (yards) from their accommodation in Nyala," UNAMID spokesman Chris Cycmanick said, adding that three gunmen in a car took them away.

An American woman working for the charity Samaritan's Purse was kidnapped almost three months ago near Nyala and remains in captivity.

Abductions of foreign workers in Sudan's violent west began in March 2009, after the International Criminal Court issued an arrest warrant for President Omar Hassan Al-Bashir for war crimes in Darfur.

The kidnappings have severely restricted the world's largest aid operation, with most foreign staff moved back to the main towns from more remote and needy areas.

The kidnappings have become a new business in Darfur with tribal leaders reporting that handsome government ransoms were paid for some hostages, fueling the abductions. Khartoum denies paying any ransom money.

Mostly young men from Arab tribes have been abducting the foreigners. Sudan has failed to prosecute anyone, despite promises to do so.

Mostly non-Arab rebels took up arms in early 2003 accusing Khartoum of neglect. A brutal counter-insurgency campaign drove some 2 million people from their homes to miserable camps, sparking one of the world's worst humanitarian crises.

The United Nations estimates some 300,000 have died in Darfur.