"We don't have confirmation of the use of mustard gas by Daesh at this time," Haq said.
Earlier in the day, Russian Foreign Ministry spokeswoman Maria Zakharova said that Moscow proposed to develop an international convention for the suppression of acts of chemical terrorism, explaining that the new instrument would transcend the issues of non-proliferation, disarmament and counter-terrorism.
In March, Russian Foreign Minister Sergei Lavrov said at the Conference on Disarmament in Geneva, Switzerland, that Moscow had called for a separate convention to cover the issue of chemical terrorism as existing international law does not fully cover the issue.
Daesh is a terrorist group that has taken control of large portions of Iraq and Syria and is outlawed in the United States, Russia and many other countries.
