Malakal , South Sudan ( CNN ) -- South Sudan forces have captured a disputed oil-rich area along the border with Sudan , escalating tensions between the two longtime rivals and threatening a return to war . Sudan claims the oil fields in the town of Heglig , which account for about half of the nation 's oil production . A spokesman for South Sudan 's military said Wednesday that his country 's soldiers have been defending the territory from attacks by Sudanese forces for the past two days . South Sudan 's military now occupies oil fields and other areas of Heglig , according to Philip Aguer , the spokesman . `` That is South Sudan , '' he said . `` Khartoum has refused to demarcate the border . We know where the border is . '' Sudan also claims ownership of Heglig and lodged complaints with the United Nations Security Council and the African Union on Wednesday , urging them to pressure South Sudan to withdraw troops from its territory . Sudan 's parliament approved `` general mobilization '' of the country 's resources to support the military . It also voted to withdraw from negotiations with South Sudan that have been ongoing since the South declared independence last July . Aguer called the parliamentary decisions `` a public relations exercise '' and accused Sudan of carrying out attacks even during the peace talks . `` There was no negotiation as far as I am concerned , '' he said . `` The SPLA ( South Sudan military ) at the border were being bombed even when the politicians were talking . '' Sudan has repeatedly bombed southern territory since independence , including the November attack of a refugee camp in the neighboring nation 's Unity state . South Sudan fought a two-decade civil war against the government in Khartoum , which led to secession . When they separated , South Sudan acquired three quarters of Sudan 's oil reserves . The two countries have been locked in negotiations about how much the landlocked South Sudan should pay to use a pipeline and processing facilities in the north . In late July , South Sudan halted oil production after accusing Sudan of `` stealing '' $ 815 million worth of its crude . Sudan said it confiscated the oil to make up for unpaid fees . The African Union-led negotiations also cover other outstanding issues since secession , including the status of citizens of both countries who find themselves living on either side of the world 's newest international border . The fate of the Abyei region and other disputed border areas are also a point of contention . Sudanese President Omar al-Bashir was scheduled to travel to the southern capital of Juba earlier this month to meet with his counterpart Salva Kiir . The presidents were to sign agreements on citizenship and border demarcation , but Khartoum canceled the trip after fighting broke out along the border . South Sudan 's sovereignty officially broke Africa 's largest nation into two , the result of a referendum last year overwhelmingly approved by voters . The referendum was part of a 2005 peace deal that ended decades of civil war pitting a government dominated by Arab Muslims in the north against black Christians and animists in the south . The war killed about 2 million people .
The oil - rich border area remains disputed between Sudan and South Sudan . Sudan claims the oil fields in the town of Heglig . The oil fields account for about half of Sudan 's oil production .