In the aftermath of the 1986 U.S. attack, the army was purged of perceived disloyal elements, and in 1988, Gaddafi announced the creation of a popular militia to replace the army and police. In 1987, Libya began production of mustard gas at a facility in Rabta, although publicly denying it was stockpiling chemical weapons, and unsuccessfully attempted to develop nuclear weapons. The period also saw a growth in domestic Islamist opposition, formulated into groups like the Muslim Brotherhood and the Libyan Islamic Fighting Group. A number of assassination attempts against Gaddafi were foiled, and in turn, 1989 saw the security forces raid mosques believed to be centres of counter-revolutionary preaching. In October 1993, elements of the increasingly marginalised army initiated a failed coup in Misrata, while in September 1995, Islamists launched an insurgency in Benghazi, and in July 1996 an anti-Gaddafist football riot broke out in Tripoli. The Revolutionary Committees experienced a resurgence to combat these Islamists.
Try to answer this question if possible (otherwise reply "unanswerable"): What chemical weapon did Libya start making in 1987?
mustard gas