evidence: It was unclear whether the comments, coming days after South Sudan seized the disputed Heglig oil field near the border, represented a formal declaration of war or were merely intended to persuade the United States, the United Nations and regional powers to force South Sudan to leave the area. [...] Ban called on South Sudan to immediately withdraw its forces from the town of Heglig, saying its seizure constituted "an infringement of the sovereignty of Sudan and a clearly illegal act." He also called on Khartoum to stop shelling and bombing South Sudanese territory and to withdraw its forces from disputed territories. [...] Since then, oil installations and areas around them are increasingly being targeted militarily. Heglig is the scene of the latest fighting. South Sudan says the Heglig oil field is within its territory, based on borders outlined in 1956 by Britain, Sudan’s former colonizer. Officials say their forces will not leave the oil field until the United Nations or the African Union sends a neutral force to oversee the area.