A leading chemical weapons expert believes it's clear the Syrian government under the Assad regime is responsible for the deadliest gas attack the country has seen since 2013, killing dozens of unprotected civilians.
The rebel-held Syrian town of Khan Sheikhoun in the Idlib province was attacked on Tuesday with a chemical agent believed to be Sarin, a colourless, odourless liquid that is generally considered to be a weapon of mass destruction.
In the hours following the attack, one of the medical clinics treating victims was hit by an airstrike. Medics, activists and witnesses on the ground said that the air strikes caused people to suffocate, while others spasmed, went pale and gasped for air, according to British-based Syrian Observatory for Human Rights sources.
WARNING: Graphic Images.
Appearing on the ABC's 7.30 on Wednesday night, Paul Walker of the non-profit NGO Green Cross International told host Leigh Sales it's time people "assume the worst".
He said if forensic evidence from a fact-finding mission launched into the attack by the Dutch organisation for the prohibition of chemical weapons (OPW) does show the Syrian government was responsible for the attack, the political repercussions could be endless.
"I think at this point we have to assume the worst, and the forensic evidence from the fact-finding mission will prove that one way or the other in the next couple of weeks," he said.
"If it does result in a forensic proof that, in fact,the Syrians attacked in the Idlib province with undeclared Sarin agent, there will be all sorts of hell to pay really, political hell to pay, from the OPW and the UN Security Council in the very near future."
While Syrian rebel forces are thought to be behind the attack, Walker said he believes it's clear the Assad regime was responsible, citing its use of the Sarin nerve agent in August 2013 in an attack on Ghouta where 1400 people were killed.
"I think it's clear this was an attack by the Syrian government. I don't think it's at all possible that the rebels had some sort of a secret chemical weapons stockpile or laboratory or production facility," he said.
"This was a nerve agent attack and the only - the only source of nerve agent we're aware of in Syria is the Syrian government which, of course, used Sarin nerve agent with incredible effectiveness in August 2013 in the Ghouta attack where over 1400 people were killed."
While the OPW fact-finding mission is still attempting to enter the country to begin its investigation, Walker also said Syria's history of discrepancies since joining the OPCW Chemical Weapons Convention hints towards their involvement.
"The Syrians did submit a declaration with the help of the OPW. This declaration has been negotiated and renegotiated and filled in and changed, probably a couple dozen times in the last four years since they submitted it," he said.
"There's been many discrepancies as the director general of the OPW has pointed out... We discovered there was a laboratory they didn't acknowledge to begin with. There were several types of chemical nerve agents, samples which were found, they had not declared."
The comments come as both Prime Minister Malcolm Turnbull and Foreign Minister Julie Bishop also called for an independent, international investigation into the attack on Tuesday.
Turnbull condemned the "horrendous use of chemical weapons".
"If the Assad regime has used chemical weapons, as is being alleged, that constitutes a war crime. It constitutes a shocking war crime," he told Tasmanian radio 7AD.
"The Assad regime should abide by the laws of armed conflict and there should be and will be I've no doubt, a full investigation into the circumstances of what appears to, well what has been, appears to be, a horrendous use of chemical weapons which we condemn."
— Tom McIlroy (@TomMcIlroy) April 5, 2017
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