The Government of India has issued a Circular No. 68/42/2018-GST dated October 05, 2018 which clarifies that the UN and specified international organizations, foreign diplomatic missions or consular posts in India, or diplomatic agents or career consular officers are entitled to claim refund as per Section 55 of CGST Act, 2017 of Compensation Cess payable on intra-State and inter-State supply of goods or services or both received by them subject to the same conditions and restrictions, mutatis mutandis, as prescribed in Notification No. 16/2017-Central Tax(Rate) dated June 28, 2017.
Further Circular can be accessed at: http://www.cbic.gov.in/resources//htdocs-cbec/gst/Circular-No-68.pdf;jsessionid=DC461CE7406C88C4CBD03B6D4C556099