Secretary of State Rex Tillerson said at the time the US had "very high confidence" that the chemical agent used in that deadly attack was sarin nerve gas. He added "they'd be ill-advised to go back to violating the chemical convention".
However, another official said that the Trump administration hopes that stepped-up global sanctions and diplomatic pressure against Damascus will help rein in Syria's chemical weapons program. This suggests that Russian Federation has been negligent in destroying the chemical weaponry as previously negotiated in 2013 as well as failed to follow through on its agreement of the UN Security Council Resolution 2209, a resolution that holds it accountable for enforcing the restriction of chemical weaponry in Syria as long as it occupies the region. "We think that they didn't carry out what they said they'd do", Mattis.
The officials also say the Islamic State group keeps using chemical weapons such as sulfur mustard and chlorine.
Mattis also said on Friday that the US government was concerned about the Syrian government's use of sarin gas, but acknowledged that he did not have evidence to prove that it was using the nerve agent. U.S. administration had alleged that Assad regime had used the banned weapon.
However, Syria and Russian Federation had rejected the USA claims, suggesting that militants might have detonated the chemical weapons on the ground.
In a statement to the Syrian state-run news agency SANA, the Syrian foreign ministry denied that it had used chemical weapons on its own people, and insisted that it had turned its chemical weapons stockpile over to the Organization for the Prohibition of Chemical Weapons.
Forces loyal to Syrian President Bashar al-Assad have continued occasional use of chemical weapons in smaller amounts since a deadly attack last April that drew a USA missile strike on a Syrian air base, the officials told reporters in a briefing.
However, Russia described the OPCW report as "very biased" arguing the report failed to address the question of who was responsible for the use of the chemical substance.
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