According to reports the officials told media persons in Washington on Thursday that President Bahsar al-Assad government has saved a part of the chemical weapons stockpile despite a US-Russian deal under which Damascus had agreed to handover all such weapons for destruction in 2014.
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.
Defense Secretary Jim Mattis says the USA has no evidence that the Syrian government has used the deadly chemical sarin on its citizens despite reports from aid groups and others in the country.
Mattis says it is clear that Assad's government has weaponized and used chlorine gas in the Syrian civil war.
"We are even more concerned about the possibility of sarin use".
President Donald Trump ordered the launch of 59 Tomahawk cruise missiles at a Syrian air base last April following a deadly sarin gas attack in Idlib, which the White House blamed on the Syrian government.
Syria has denied using illegal chemicals.
"You all have seen how we reacted to that, so the Syrian government would be ill-advised to go back to violating the chemical convention", Mattis said.
It quoted residents and medical sources as saying "toxic gas" was used in the attack, without elaborating.
Syria's Foreign Ministry has dismissed as "null and void" USA accusations that President Bashar Assad's government is producing and using "new kinds of weapons" to deliver deadly chemicals despite committing to abolish its program in 2013.
Syria on Saturday denied recent accusations by the United States that it had used chemical weapons on opposition forces near the capital Damascus, shrugging them off as "lies", AFP reported.
The Syrian Foreign Ministry has rejected the United States claims about the Syrian government using chemical weapons in the war as "lies". Make a donation and help pay for our journalism.