When Musa became self-proclaimed sultan in European part of the Ottoman Empire, he attacked Serbia in early 1412 but was defeated by Stefan near Novo Brdo in Kosovo. Stefan then invited the ruler of the Anatolian part of the empire, sultan Mehmed Çelebi to attack Musa together. Securing Hungarian help, they attacked Musa on 5 July 1413 at the Battle of Çamurlu, near the Vitosha mountain (modern Bulgaria) and defeated him, with Musa being killed in the battle. As a reward, Stefan received the town of Koprijan near Niš and the Serbian-Bulgarian area of Znepolje. For next twelve years, Stefan remained in good relations with Mehmed, which made the recovery of medieval Serbia possible.