According to Russian media, Daesh militants have used sulfur mustard gas, a chemical warfare agent, at least three times in Syria and Iraq since the beginning of the current year, the head of the Russian Foreign Ministry's department on arms control said Tuesday.

'In spite of the many crimes involving the use of chemical weapons that have been committed by terrorists on the territory of Syria and Iraq, the United Nations Security Council has not responded yet. It is becoming harder and harder to block the Russian proposals under the pressure of facts. According to our data, Daesh militants used the sulfur mustard at least three times in the first quarter of 2016. This is a dangerous chemical agent, the use of which is a serious crime,' Mikhail Ulyanov told RIA Novosti.

The statement comes a day after a military source told RIA Novosti that Daesh used a chemical substance in an attack against a Syrian army airbase in the province of Deir Ez-zor.

In March, Russian Foreign Minister Sergei Lavrov said at the Conference on Disarmament in Geneva that Moscow calls for a separate convention to cover the issue of chemical terrorism as the existing international law does not solve the issue; IRNA reported.

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