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. However, they declined to provide specific details about the alleged Damascus moves for developing or maintaining chemical weapons. That strike followed a deadly chemical weapons attack by Assad's government.
Raising the alarm about the continued threat, United States officials said it was "highly likely" that Assad kept a hidden stockpile of chemical weapons after 2013 that he failed to properly disclose.
He was of the opinion that if worldwide community does not act quickly to tighten the screws on Mr Assad, Syria's chemical weapons could spread beyond its borders and possibly even "to USA shores". "They think they can get away with it if they keep it under a certain level", the official said.More news: Putin congratulates Finland's Niinisto on presidential win
Mattis also said on Friday that the USA 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.
The US is concerned about the potential use of sarin gas in Syria, US Defense Secretary Jim Mattis said on Friday, a day after Washington warned it was prepared to consider military action if necessary to deter chemical weapons attacks by the Syrian government. "What I am saying is that other groups on the ground - NGOs, fighters on the ground - have said that sarin has been used, so we are looking for evidence". Mattis hinted at such action on Friday, referencing a US missile strike on a Syrian military airfield previous year. However, he acknowledged of not having seen evidence of the nerve agent sarin used by the Syrian government. Unlike sarin, chlorine gas is relatively easy to produce and is not banned by the Chemical Weapons Convention.