He said that two months after more than USD 4.5 billion were pledged for Sudan at the Oslo's donor conference, a large amount of that pledge has "yet to be converted into cash," and more pledges for immediate assistance are urgently needed to feed more than six million people during the next few months.
He said the hunger period is already taking its toll in Darfur, with malnutrition rates on the rise in several areas.
"These trends must be reversed and our achievements sustained, requiring a relief effort of epic proportions," he said.
"If we fail to respond to these challenges now," he warned, "the political consequences could haunt us for many years. Most worryingly, the main hope for peace in Sudan as a whole - the Comprehensive Peace Agreement - could be placed in serious jeopardy."
He called for the urgent establishment of a civil administration in south Sudan.
"If those returning to the south cannot sustain themselves, and are forced to leave a second time, confidence in the peace will be dealt a serious blow," he cautioned.
"Much has been said about the historic opportunity presented by the Comprehensive Peace Agreement, and about the importance of an immediate peace dividend to its successful implementation. Now is the time for all donors to deliver," he said.