The Kra Isthmus in Thailand is the narrowest part of the Malay Peninsula. The western part of the isthmus belongs to Ranong Province and the eastern part to Chumphon Province, both in Southern Thailand. The isthmus is bordered to the west by the Andaman Sea and to the east by the Gulf of Thailand. The Kra Isthmus marks the boundary between two sections of the mountain chain which runs from Tibet through the Malay peninsula.