Sudan's President Omar al-Bashir has ruled out talks with South Sudan on the simmering border conflict that has prompted fears of all-out war. He was speaking during a visit to the major oilfield and border town of Heglig, which was occupied by South Sudanese troops nearly two weeks ago. South Sudan says it has withdrawn from Heglig, but Sudan says its army forced them out. Earlier, Sudanese jets bombed a border area in South Sudan, witnesses said. "We will not negotiate with the South's government, because they don't understand anything but the language of the gun and ammunition," Reuters news agency quoted Mr Bashir as telling troops on his arrival in Heglig. The past few months have seen sporadic fighting in the oil-rich areas along the two countries' undemarcated border, prompting concern the violence could escalate into a full-blown war. US President Barack Obama has said both countries "must have the courage" to return to the negotiating table and resolve their differences peacefully. 'Declaration of war' On Monday, Sudanese warplanes dropped bombs near the South Sudanese border town of Bentiu, killing at least one person, according to witnesses. Taban Deng, governor of Unity State, said the bombs fell on a key bridge, which leads to the border, and a market between the state capital Bentiu and the nearby town of Rubkona. The witnesses described seeing a huge plume of smoke rising from a market and the body of a dead boy. Mr Deng said that three civilians had also been critically wounded in the raid and were not expected to survive. South Sudan's deputy head of intelligence, Mac Paul, described the bombing as a "declaration of war", according to the Associated Press. The attack was condemned by the UN peacekeeping mission in South Sudan and the United States, which called for an immediate end to violence. A foreign ministry official in Khartoum denied that Sudan had carried out the raid, according to AFP. Following months of border skirmishes, South Sudan sent its forces into Heglig earlier in April, saying the area was being used as a base for Sudanese attacks on its territory. Heglig, which used to provide more than half of Sudan's oil, is internationally accepted to be part of Sudanese territory, but the border area is yet to be demarcated. South Sudan says the area should belong to it, and that the issue should be resolved by international mediation. Mr Bashir responded to the seizure of Heglig by saying that his main goal was now to "liberate" the people of South Sudan from its rulers, describing the former rebel Sudan People's Liberation Movement (SPLM) government in Juba as "insects" that needed to be eliminated. The UN Security Council demanded that Juba withdraw its forces from Heglig and the neighbouring Abyei regions, as well as a "complete, immediate, unconditional" end to all fighting. It also called on Sudan to stop aerial bombing raids on South Sudanese territory. On Sunday, South Sudan's army said its withdrawal from the area was complete. Satellite pictures of the Heglig area released on Sunday suggest key oil installations were badly damaged in the fighting and are no longer operating. The former rebel Sudan People's Liberation Movement (SPLM) has governed South Sudan since it seceded from Sudan after an overwhelming vote in favour of independence in a July 2011 referendum. The vote was the outcome of the 2005 Comprehensive Peace Agreement, which put an end to the 22-year civil war between the former north and south of Sudan. About 1.5 million people are though to have lost their lives in the conflict. The new state took most of the former united Sudan's oil reserves with it, but relies on pipelines to seaports in Sudan to export it. In January, South Sudan decided to shut down oil production, which provides 98% of the government's revenue, after Khartoum impounded South Sudanese oil shipments amid a dispute over transit fees.