War in Sudan's South Kordofan and Blue Nile states has affected an estimated 900,000 people, but more than a year of talks has failed to get food aid into rebel zones, the UN said on Friday."In Sudan People's Liberation Movement-North (SPLM-N) areas, no humanitarian staff have been able to enter from within Sudan and no food aid has been delivered, despite intensive negotiations that have been going on now for more than 16 months," the Office for the Coordination of Humanitarian Affairs (OCHA) said.In one of its most strongly worded statements on the situation in the two states bordering South Sudan, OCHA said a joint initiative by the UN, Arab League and African Union for assessment and aid delivery throughout the war zone is still awaiting a "green light.""Efforts to gain access to war-affected civilians have been relentless," said OCHA.The so-called Tripartite proposal was issued in February, agreed to by the SPLM-N rebels that same month, and by the Khartoum government in June.Two months ago, the government and rebels each signed memorandums with the Tripartite group to facilitate aid delivery."Despite various different detailed action plans that have been presented by the Tripartite since then, neither the government nor the SPLM-N have yet formally agreed on a concrete plan of action for assessment and delivery of aid," OCHA said."The Tripartite has made clear that it is ready to facilitate the immediate provision and distribution of humanitarian assistance once the government and the SPLM-N agree to the plan and provide the necessary security guarantees."