Following the 1991 Gulf War, as part of the ceasefire agreement, the United Nations Security Council Resolution 687 mandated that Iraqi chemical, biological, nuclear, and long range missile programs be halted and all such weapons destroyed under United Nations Special Commission control. The UN weapons inspectors inside Iraq were able to verify the destruction of a large amount of WMD-material, but substantial issues remained unresolved in 1998 when the inspectors left Iraq due to then current UNSCOM head Richard Butler's belief that U.S. and UK military action was imminent. Shortly after the inspectors withdrew, the U.S. and UK launched a four-day bombing campaign in Iraq.