The State Department said it was assessing indications that the regime used chemical weapons on Sunday during its offensive in Idlib, the most significant remaining holdout of rebels.
The United States sees signs the Syrian regime may be using chemical weapons, including an alleged chlorine attack on Sunday in northwest Syria, the State Department said on Tuesday, warning that Washington and its allies would respond "quickly and appropriately" if this were proven.
"Unfortunately, we continue to see signs that the Assad regime may be renewing its use of chemical weapons, including an alleged chlorine attack in northwest Syria on the morning of May 19," State Department spokeswoman Morgan Ortagus said in a statement.
"We are still gathering information on this incident, but we repeat our warning that if the Assad regime uses chemical weapons, the United States and our allies will respond quickly and appropriately," she said.
Ortagus said the alleged attack was part of a violent campaign by Bashar al Assad's forces violating a ceasefire that has protected several million civilians in the greater Idlib area.
TRT World spoke to James Farwell, a senior fellow at Middle East Institute, for his take on the issue.
Attacks 'must end'
"The regime’s attacks against the communities of northwest Syria must end," the statement said. "The United States reiterates its warning, first issued by President Trump in September 2018, that an attack against the Idlib de-escalation zone would be a reckless escalation that threatens to destabilise the region."
President Donald Trump's administration has twice bombed Syria over Assad's alleged use of chemical weapons, in April 2017 and April 2018. In September, a senior US official said there was evidence showing chemical weapons were being prepared by Syrian regime forces in Idlib, the last major rebel stronghold in the country.
The State Department statement accused Russia and Assad's forces of "a continuing disinformation campaign ... to create the false narrative that others are to blame for chemical weapons attacks."
"The facts, however, are clear," the statement said. The Assad regime itself has conducted almost all verified chemical weapons attacks that have taken place in Syria — a conclusion the United Nations has reached over and over again."
A US official, speaking on the condition of anonymity, said the Syrian regime had a history of resorting to chemical weapons when fighting intensified. The official, however, was not aware of any confirmation of what substance was allegedly used, if at all, and said the US government was still gathering information.
There was no immediate comment from the Syrian regime on the US statement.
In March, Syrian regime media cited a hospital in regime-held Hama as saying 21 people suffered choking symptoms from poison gas after rebels shelled a village.
In January, US national security adviser John Bolton warned the Syrian regime against using chemical weapons again.
“There is absolutely no change in the US position against the use of chemical weapons by the Syrian regime and absolutely no change in our position that any use of chemical weapons would be met by a very strong response, as we've done twice before," Bolton said at the time.
Fresh Idlib clashes leave 44 dead
Rebels launched a counterattack against regime forces Tuesday on the edges of their bastion in northwestern Syria, leaving dead 26 pro-regime fighters and 18 rebels, a monitor said.
The rebel-dominated Idlib region is nominally protected by a buffer zone deal, but the regime and its Russian ally have escalated their bombardment of it in recent weeks, seizing several towns on its southern flank.
Syria's former Al Qaeda affiliate, Hayat Tahrir al Sham, controls a large part of Idlib province as well as adjacent slivers of Aleppo, Hama and Latakia provinces.
Rebels on Tuesday launched a counterattack against pro-regime positions to the south of the enclave, the Syrian Observatory for Human Rights said.
The fighting in the town of Kafr Nabuda in the north of Hama province killed 26 pro-regime fighters, as well as 18 rebels, the Britain-based monitoring group said.