GENEVA, July 3 (Reuters) - The United Nations human rights chief on Friday said another human rights catastrophe was unfolding in Sudan, in the city of al-Obeid in North Kordofan, and urged the world to act. "The signs from al-Obeid are clear and unmistakable: Another human rights catastrophe is unfolding in Sudan, this time in the capital of the strategic state of North Kordofan," the U.N. high commissioner for human rights Volker Turk told delegates in Geneva during an urgent debate at the U.N.