UN to visit Syria airbase in Khan Sheikhoun gas attack probe
Some Western diplomats have expressed scepticism however, suggesting Damascus will use the visit to bolster its claim that the sarin gas was released by an accidental airstrike on a storage depot.
The joint investigation of the United Nations and the Organisation for the Prohibition of Chemical Weapons (OPCW) was set up in 2015 by the Security Council to determine who is behind chemical weapons use in Syria.
The JIM has already determined that Syrian regime forces were responsible for chlorine attacks on three villages in 2014 and 2015, and that Islamic State militants used mustard gas in 2015.
The OPCW presented a report confirming sarin gas was used in the attack at Khan Sheikhoun earlier this year, but did not assign blame, leaving that determination to the JIM.
In total, OPCW is investigating as many as 45 suspected chemical attacks in Syria since mid-2016 including the recently-disclosed use of sarin on an opposition-held village on March 30.
The United States, France and Britain are facing a showdown with Russia over the fate of the gas attacks investigation when the JIM's mandate comes up for renewal in the coming weeks.
US Ambassador Nikki Haley last week said allowing the JIM to continue its investigations of gas attacks in Syria should be a "top priority" for the Security Council.