UN Secretary General Antonio Guterres is calling for an immediate end to what he calls a 'nightmare of violence' in Sudan. Last week, the paramilitary Rapid Support Forces (RSF) seized the besieged city of el-Fasher from the Sudanese Army Forces (SAF). It's a major turning point in Sudan's war - cementing RSF control of the western Darfur region. Since then, horrifying reports have been emerging from el-Fasher. The RSF is accused of carrying out mass executions and other atrocities. Satellite