The Nicobar Islands are an archipelagic island chain in the eastern Indian Ocean and one of the most isolated in the world. They are located in Southeast Asia, 150 km north of Aceh on Sumatra, and separated from Thailand to the east by the Andaman Sea. Located 1,300 km southeast of the Indian subcontinent, across the Bay of Bengal, they form part of the Union Territory of Andaman and Nicobar Islands, India. UNESCO has declared the islands as one of the World Network of Biosphere Reserves.