New York - Sudan's government is stepping up pressure on the United Nations as Secretary General Ban Ki-moon prepares recommendations on the future of a joint UN-African Union peacekeeping force in the country's violence-wracked Darfur region.In the government's latest move, President Omar al-Bashir ordered the expulsion of two top UN officials, a decision condemned by the secretary general on Thursday as "unacceptable". The UN chief called on Sudan's government to reverse its decision immediately.So did US Ambassador Samantha Power who tweeted on Friday: "Sudan gov continuing to show true colors: expels 2 UN officials while violence continues. Shameful decision should be reversed."The expulsions follow al-Bashir's call on 30 November for a "clear programme" to end the joint mission in Darfur, known as Unamid, which was established in 2007 to protect civilians caught in a conflict between rebels who took up arms against the government in 2003, accusing it of discrimination and neglect. The United Nations says 300 000 people have died in the conflict and more than two million have fled their homes.Recently, Al-Bashir also ordered Unamid's human rights office to close and refused to allow the force to make a second visit to the north Darfur village of Tabit to investigate allegations that more than 200 women were raped there by forces allied to the government. Their initial visit found no evidence, but there were allegations that local people were intimidated by the presence of Sudanese soldiers.Power, the US envoy, also tweeted: "2.4M ppl in Darfur need aid & protection. Sudan government is willfully obstructing UN & NGO efforts to save lives."UN spokesperson Stephane Dujarric said on Friday that the secretary general is working on the strategic review of Unamid ordered by the Security Council on 27 August. UnderperformanceThe joint peacekeeping mission — with nearly 16 000 military, over 3 000 police, and more than 4 000 civilian staff — has the second-highest budget of all UN peacekeeping forces, at more than $1.3bn a year. But it has been criticised for under-performance."It has the largest gap between the resources that are put into the mission and the effect it has had on the ground," Britain's UN ambassador, Mark Lyall Grant, told reporters in April when the Security Council adopted a resolution aimed at streamlining Unamid's functions.In another sign of discontent, Ban said he was "deeply troubled" by the findings in a UN report released in late October that Unamid took an "unduly conservative" approach to publicly sharing information about crimes against civilians and peacekeepers.The Security Council resolution adopted in August asks the secretary general, in close consultation with the African Union, to present recommendations "for the future mandate, composition, configuration and exit strategy of Unamid" by 28 February 2015. It also asks Ban to present a road map of tasks now done by Unamid that can be transferred to the UN country team in Sudan, which includes about 1 000 civilians who focus on humanitarian operations, development and other non-military issues.Al-Bashir's expulsion order this week was against top officials from the country team — UN Resident Co-ordinator Ali Al-Za'tari, a Jordanian, and the UN Development Programme's Country Director Yvonne Helle, from the Netherlands, Dujarric said.Akshaya Kumar, a policy analyst at the US-based Enough Project, which campaigns to end crimes against humanity in Darfur, said the expulsions are part of the government's campaign "to create an incredibly hostile environment for the United Nations in country".Unfortunately, Kumar said, Unamid hasn't increased its effectiveness in protecting civilians since April. But she warned that pulling peacekeepers out would be dangerous because it would be "kowtowing to this series of brinksmanship acts by the Sudanese government".