AS Kofi Annan spends his last working day at the United Nations he will doubtless reflect on his failure to secure the Sudanese government's unequivocal agreement to the presence of a UN peacekeeping force in its benighted Darfur region. Along with the intense and ultimately successful negotiations to bring the Israel-Lebanese war to a halt in the summer, the Darfur situation has been Mr Annan's top priority throughout much of his last year as Secretary General. In March this year it seemed that the Sudanese government had signed a tortuously negotiated agreement among all the parties to the Darfur fighting that provided for a UN force; however, Khartoum's commitment proved to be provisional and since then there have several more false dawns while the killing, raping and plunder continued. Last weekend Mr Annan said that he believed a satisfactory letter was on its way from the Sudanese president, Omar Hassan a-Bashir, but it has turned out to be another disappointment, limiting UN involvement to “backstopping, and logistical and technical support” for the inadequate number of African Union forces already deployed in Darfur. Perhaps in order not to make matters more difficult for his successor, Mr Annan generously described this letter as “encouraging”. But as he clears his desk this afternoon Mr Annan will surely regret that during his decade as Secretary General an increasing number of nations have seen fit to ignore or obstruct the authority of his office.