The head of the international watchdog for chemical weapons warns that strikes on Syrian chemical weapons sites could contaminate and destroy valuable evidence. The Organisation for the Prohibition of Chemical Weapons (OPCW) is closely monitoring reports of strikes on military facilities but does not yet know if chemical weapons sites have been affected. The director-general of the OPCW, Fernando Arias, also highlights the risk of losing control over dangerous chemicals or equipment. The OPCW has been investigating chemical weapons use in Syria since 2014 and has issued 21 reports on alleged instances of use.