The ultimate authority for actions taken to remove Iraq's weapons of mass destruction derives from Security Council Resolution 687, which decided that Iraq "shall unconditionally accept the destruction, removal, or rendering harmless under international supervision" of its weapons of mass destruction and long-range missiles. This remains the position.
The onus was on Iraq firstly to present a full list of its banned weapons and then to produce all weapons on that list for destruction. Resolution 687 established UNSCOM as a special commission of the Security Council, and mandated its arms inspectors to verify Iraq's compliance with those requirements and to destroy all weapons produced.
Security Resolution 1284 established the successor of UNSCOM, UNMOVIC, as a subsidiary body of the Security Council, with the same mandate as UNSCOM and increased powers and responsibilities in relation to enforcing Iraq's compliance with its obligations.