Shells hit a United Nations base in Sudan\'s troubled South Kordofan state on Friday killing one Ethiopian peacekeeper and wounding two others, officials said. Residents suspect stray fire hit the base and that anti-government rebels had targeted a football stadium to be used for a regional tournament starting on Tuesday. Khartoum accuses neighbouring South Sudan of backing the Sudan People\'s Liberation Movement-North (SPLM-N) rebels in South Kordofan. Tensions between the two have escalated this week, endangering a vital oil deal. \"I condemn this shelling, which killed one peacekeeper and injured two others,\" UN leader Ban Ki-moon said, urging Khartoum and the SPLM-N to immediately cease hostilities and resume ceasefire negotiations. A UN Security Council statement \"condemned in the strongest terms\" the attack and called on the Sudanese government to \"bring the perpetrators to justice.\" The three Ethiopian victims are part of the UN\'s Interim Security Force for Abyei (UNISFA), a nearby area disputed by Sudan and South Sudan, the UN said. UNISFA has a logistics base in Kadugli. Ban said two shells hit the office of a joint Sudan-South Sudan-UNISFA unit tasked with monitoring a border buffer zone. Sudan last Sunday said it was freezing an oil deal, a buffer zone pact and seven other deals with South Sudan over alleged backing for rebels. The SPLM-N have been fighting Sudanese forces for two years in South Kordofan, which the UN says faces a major humanitarian crisis. The rebels could not be reached for comment on Friday but they have periodically shelled Kadugli since late last year, causing some fatalities. After the attack, about 20 staffers from various UN agencies in Kadugli sought protection at the World Food Programme office, WFP spokeswoman Amor Almagro said. Rebels last targeted Kadugli in late April when they fired on the airport area. \"The funny thing is that this was the safest area in Kadugli,\" one resident told AFP, asking for anonymity. \"I think they were targeting the stadium and the police base near the stadium.\" Another resident said he heard heavy weapons fire at the same time as the shelling and the aim was to \"disrupt\" the CECAFA Club Cup tournament. Kenyan champions Tusker were scheduled to play in the opening day match in Kadugli but announced on June 6 that they were pulling out because of safety fears. Kadugli is co-hosting the tournament with El Fasher in Sudan\'s war-torn Darfur region. Tanzania\'s government warned two teams from that country against travelling to Darfur for their matches. South Kordofan state governor Ahmed Haroun told worshippers at a Kadugli mosque on Friday that CECAFA \"will continue\", said a resident who was at the mosque. Sudanese state security officers this week refused an AFP reporter permission to travel to Kadugli for the football matches. Friday\'s attack comes a day after Sudan\'s army blamed Darfur rebels allegedly backed by South Sudan for an explosion and fire in an Abyei oil pipeline. Both South Sudan and the Justice and Equality Movement (JEM) insurgents denied any involvement. JEM accused the government itself of being behind the attack. The oil ministry on Friday said the line was already being reconstructed. JEM belongs to the Sudan Revolutionary Front rebel coalition with the SPLM-N, which is also fighting in Blue Nile state. Analysts say the coalition humiliated authorities with recent attacks before Khartoum\'s petroleum ministry on Tuesday formally told oil companies to block exports of South Sudanese crude within 60 days. Under a peace deal which ended a 22-year civil war, South Sudan separated in 2011 with most of Sudan\'s oil production. The export infrastructure remains under northern control. Khartoum will not allow the South\'s export revenue \"to be used in support of rebels against Sudan\", President Omar al-Bashir said.