The Secretary-General shall act in that capacity in all meetings of the General Assembly, of the Security Council, of the Economic and Social Council, and of the Trusteeship Council, and shall perform such other functions as are entrusted to him by these organs. The Secretary-General shall make an annual report to the General Assembly on the work of the Organization.

High

Article 98, Chapter XV, Charter of the United Nations
http://www.un.org/en/sections/un-charter/chapter-xv/index.html