They singled out Russian Federation, echoing comments from Secretary of State Rex Tillerson and other USA leaders who have said Moscow bears responsibility for the chemical attacks.
The officials reiterated US Secretary of State Rex Tillerson's recent accusation that Russia, Mr Assad's ally in Syria's multi-sided civil war, bears some responsibility for failing to enforce the chemical weapons ban. The Syrian Observatory for Human Rights said three people suffered respiratory problems after a rocket attack.
"We are on the record and you all have seen how we reacted to that, so they would be ill-advised to go back to violating the chemical (weapons) convention", Mattis said.
But the officials stopped short of promising additional military action to halt Syria's use of chemical weapons.
The worker behind Hawaii's missile scare thought there was a real missile
The Hawaii state report revealed that the worker had confused real events with practice drills in the past as well. The emergency management agency provided the FCC with information from a written statement from the officer.
The senior US officials, speaking to journalists on the condition of anonymity because they were not authorized to speak publicly, said there did not appear to have been any "large use" of banned munitions since April.
"Deterrence is something that you have to continually work at", said the second official.
However, a senior official said the Trump administration is hopeful this time that more sanctions and diplomatic pressure will help eliminate Assad's chemical weapon program, Reuters reported.
But while the Trump administration has resolved to punish Syria's use of chemical weapons with military force, a change in tactics from Damascus may complicate things. The scientists said the samples also matched those taken from the site of another alleged chemical attack past year.
EasyJet chief cuts salary as airline reveals 52% gender pay gap
In the United Kingdom , employers with more than 250 employees are required to disclose their payrolls to the government by April. So let's call this an important start - both in message and in action - aimed at keeping the critical conversation going.
The officials said Syria's most recent alleged chemical weapons attack suggests President Bashar Assad's regime is developing more sophisticated weapons, according to the Associated Press.
But the officials said the USA believes Assad's government sees chemical attacks as an effective way to terrorize rebels and sympathetic populations into fleeing, therefore altering the demographic balance in the Alawite heartland where Assad is trying to consolidate control. "And that use will spread to USA shores".
In a recently released annual report, the White Helmets said that as many as 1,337 civilians had been killed in Eastern Ghouta a year ago amid ongoing attacks by regime forces.
Battle for Azeroth launches this Summer
Or are you skipping this one out? These races include the Highmountain tauren , Lightforged draenei , Nightborne, and Void elves . Thankfully, these requirements are account-wide, helping Alliance players unlock the Horde races fairly easily and vice versa.