Volker Turk, the United Nations human rights chief, warned on Friday of a human rights catastrophe unfolding in el-Obeid, the capital of North Kordofan state in Sudan. The Sudanese Armed Forces and Rapid Support Forces are fighting for control of surrounding areas in a war that began more than three years ago and has produced a broad humanitarian crisis. Several details, including the duration of reported siege conditions and the setting of the statement, remain unverified.