After the Mongol Prince Köden took control of the Kokonor region in 1239, he sent his general Doorda Darqan on a reconnaissance mission into Tibet in 1240. During this expedition the Kadampa monasteries of Rwa-sgreng and Rgyal-lha-khang were burned, and 500 people killed. The death of the Mongol qaghan Ögedei Khan in 1241 brought Mongol military activity around the world temporarily to a halt. Mongol interests in Tibet resumed in 1244, when Prince Köden sent an invitation to the leader of the Sakya sect, to come to his capital and formally surrender Tibet to the Mongols. The Sakya leader arrived in Kokonor with his two nephews Drogön Chögyal Phagpa ('Phags-pa; 1235–80) and Chana Dorje (Phyag-na Rdo-rje; 1239–67) in 1246. This event marked the incorporation of Tibet into the Mongol Empire. Tibet was under administrative rule of the Yuan dynasty until the 1350s. At that point, Tibet regained its independence.