Sudanese soldiers leave the Heglig oil field in Sudan, April 23, 2012. Border clashes between the two neighbors have been ongoing since South Sudan won independence in July 2011, and the South seized Sudan's most important oil field in Heglig on April 10 and occupied it for ten days, sparking strong international condemnation. On April 20 the Sudanese army announced the liberation of Heglig, which includes Sudan's biggest oil fields, after bloody battles with South Sudan army. [Xinhua]