The spokesman for the joint U.N.-African Union peacekeeping force in Darfur says the Sudanese government has asked his mission to prepare plans to exit the country.

The snub comes amid tension between the mission and the government over an investigation into allegations of mass rape in the violence-torn western region of Darfur. Initially, the mission was denied access to Tabit, a North Darfur village where allegations surfaced in media that women were raped by government-allied troops. Following a brief visit, escorted by government troops, the mission said it had not immediately discovered evidence of rape.

Spokesman Ashraf Eissa said Sunday the formal memo to leave was delivered last week. The mission's mandate expires in March. The U.N. Security council asked the organization's secretary-general to prepare an exit strategy by February.