Four members of the Ethiopian contingent to a U.N. peacekeeping mission in Sudan were killed Tuesday in the disputed region of Abyei. Ethiopian members of the newly created U.N. Interim Security Force for Abyei were on patrol in the region when they struck a land mine. Four soldiers were killed and seven others were injured, the United Nations said. U.N. Secretary-General Ban Ki-moon in a statement expressed condolences to family members and the Ethiopian government. South Sudan became the world's newest independent nation July 9. Its secession from Sudan came through a peace deal reached in 2005 that ended a civil war in the region. Issues such as citizenship, the sharing of oil revenue and border demarcation are unsettled. Border conflicts centered on Abyei and South Kordofan state threaten the principles of the peace agreement. Alain Le Roy, U.N. undersecretary-general for peacekeeping operations, told the U.N. Security Council that hundreds of peacekeepers deployed to Abyei in Sudan as part of the UNISFA in July. He said there were outstanding issues over jurisdiction in the area, however. More than Ethiopian 500 troops were sent to the region since UNISFA was established in June.