Under the terms of the cease-fire, all missiles with a range over 150 km as well as all R&D, support and manufacturing facilities, are to be dismantled, and Iraq is prohibited from using, developing, constructing or otherwise acquiring ballistic missiles over that range in the future. After the Gulf War, the 61 missiles that Iraq had acknowledged remained in its arsenal were destroyed; the head of the UN mission in charge of the task said that the UN had no evidence indicating that the Iraqis possess any other missiles. However, to alleviate any lingering doubts, the Special UN Commission is mandated by Res. 687 to develop a long-term plan for the ongoing monitoring and verification to ensure Iraqi compliance with its terms.
Since the end of the Gulf War, UN inspection teams worked to find evidence that Iraq has hidden a residual Scud force of 100-200 missiles and 12-20 launchers. In March 1993, Rolf Ekeus, chairman of the U.N. Commission charged with eliminating Iraq's weapons that are in violation of Resolution 687, said that inspectors were unable to account for 200 of Iraq's 800 Scuds. As time past without discovering this putative residual force, the question turned to how quickly these hidden Scuds could be brought to a state of military readiness. The East German army considered that if kept in the maufacturers containers with partial guidance systems installed the Scud could be assembled after 20 years of storage and be ready for fuelling in about 95 minutes. Consequently, the US was concerned that if UN sanctions were lifted before there was high confidence that all Scuds and other potential WMD are eliminated, Iraq could quickly renew its threat to the Gulf region and in a few years regain its missile development and production capacity. A similar concern pertained to Iraq's residual nuclear, chemical, and biological weapons programs that may be eluding UN Inspectors.

"Earlier ambiguity concerning Iraq's residual missile inventory has been largely resolved, though UNSCOM maintains that Iraq is still concealing six to sixteen enhanced Scud missiles, potentially able to deliver chemical or biological warheads. These Al Hussein missiles have eluded UNSCOM inspectors, along with as many as 20 long-range missile warheads produced before 1991 specifically to carry biological weapons. Iraqi is also known to have biological gravity bombs and tons of VX nerve gas. By 1996 UNSCOM concluded that Iraq had produced 80 Scud-like missiles indigenously -- thereby placing in doubt UNSCOM's initial overall count of Iraq's original missile inventories. UNSCOM teams visiting in 1996 have been unable to locate hidden missiles but UNSCOM has been investigating Iraq's methods of concealment. "

http://www.fas.org/nuke/guide/iraq/missile/unscom.htm