Muslim Berbers called the Rif (Riff), who inhabited the er-Rif region in northern Morocco, menaced the Spanish possessions there along the Mediterranean coast. When Morocco's sultan failed to check the Rif, Spain fortified its Melilla enclave, which was soon besieged by Rif tribesmen. The attack plus the killing of Melilla's military commander caused a severe public outcry in Spain, and in November 1893, a 25,000-man force was sent to Melilla and eventually drove the Rif back. By the Treaty of Fez (1894) the sultan agreed to pay Spain a war indemnity of 20 million pesetas and to punish the Rif. In addition, Spain could proceed with its fortification of Melilla, where a buffer zone was established between it and Morocco.