S. Sudan, Sudan fighting escalates JUBA, South Sudan, April 18 (UPI) -- Nearly two dozen soldiers were killed during fighting along the Sudan-South Sudan border, a military spokesman said. Fighting between rival forces about 100 miles west of the Heglig oil field left seven South Sudanese soldiers and 15 troops from Sudan dead, a spokesman for the South Sudanese military told the BBC. South Sudanese forces last week seized Heglig, which Sudan claims as its sovereign territory. South Sudan gained independence last year under the terms of a 2005 peace deal though borders weren't formally demarcated. Former South African President Thabo Mbeki, serving as a mediator to the crisis, and Haile Menkerios, U.N. assistant secretary-general for political affairs, told the U.N. Security Council this week that the Sudanese and South Sudanese governments were controlled by hard-liners, the BBC reports. South Sudanese President Salva Kiir said he wasn't obligated to U.N. demands to pull his forces from Heglig. Sudanese President Omar al-Bashir is wanted for war crimes in connected to the genocide in Darfur. Diplomats told the Security Council that both sides were "locked in a logic of war," the BBC said.