GENEVA (Reuters) - U.N. agencies are planning for the possible arrival of 200,000 refugees in Sudan fleeing violence in Ethiopia over a six-month period, U.N officials said on Friday, with one voicing fears that the burden could “unravel” its neighbour. Hundreds, possibly thousands, of people have died since Ethiopian government troops launched a war two weeks ago in northern Tigray state against regional authorities they accused of staging a surprise attack on federal forces. Thousands of refugees have fled, some crowding into boats to cross a river to Sudan, overwhelming aid groups positioned on the other side. “Together with all the agencies we have built a response plan for about 20,000 people and currently we are at about 31,000 so it has already surpassed that figure,” UNHCR’s Axel Bisschop told a Geneva briefing. “The new planning figure is around 200,000.” Another UNHCR official called for a temporary ceasefire with immediate effect to allow for humanitarian corridors. UNICEF’s Sudan-based representative Abdullah Fadil voiced fears about the impact of the arrivals on a country already facing major economic and political challenges and hosting 1 million refugees from other African neighbours.“Our serious concern is if we do not act quickly with the resources needed...this could unravel not only Ethiopia but also Sudan,” he told the same briefing. U.N. agencies are seeking $50 million in immediate funding which will go towards providing food and setting up new camps as part of a broader plan to secure $200 million. Fadil raised concerns about disease spreading amongst the crowds, of whom nearly half are children.