This frame grab from video provided on Tuesday April 4, 2017 shows a Syrian doctor treating a boy following a suspected chemical attack, in the town of Khan Sheikhoun, northern Idlib province, Syria.
Damascus, along with its Russian and Iranian allies, has said that the April 4 casualties were caused when a conventional air strike on an al-Qaeda weapons depot nearby caused an explosion, releasing the deadly gases.
The incident with chemical weapons in Idleb was "made up, " Syria " s presidential advisor Bouzeina Shabaan said in an interview with Al Mayadeen channel published today in Damascus".
The Syrian regime and its backers, including Russian Federation, have denied Mr Assad was responsible.
The UN mediator for Syria said on Thursday he would hold talks with Russian Deputy Foreign Minister Gennady Gatilov in Geneva on Monday and that the United States had declined to take part in any trilateral meetings for now.
The Organisation for the Prohibition of Chemical Weapons' Director General Ahmet Uzumcu said results of the analysis "indicate that sarin or a sarin like substance was used".
Mikhail Uliyanov, the head of the Russian Foreign Ministry's department for Nonproliferation and Arms Control (DNAC) said earlier on Thursday that the OPCW inaction over chemical weapons incident could damage its credibility as there are no facts that OPCW representatives have visited the Khan Sheikhoun area.
The Belgian representative said the fact-finding team deserved the OPCW's full confidence and there was no need "to put in place a new structure".
"If there really was sarin in Khan Sheikhoun, how can the OPCW explain White Helmets charlatans jumping in sarin vapor without protection means?"
The Syrian government has moved nearly all of its operational aircraft - both jets and helicopters - to a Russian airbase in Syria for protection from another possible round of US airstrikes, Fox News has confirmed.
That would have enabled Moscow to deploy its own experts alongside the OPCW's independent teams in a bid "to discredit the results" so far, one source close to the discussions told AFP.
In an unprecedented step, the OPCW's executive council in November condemned Syria's use of toxic weapons - the council's first open condemnation of a member of the Chemical Weapons Convention.
Islamic State jihadists were also found to have used mustard gas in August 2015 in Syria.
It pointed out that its mandate was to investigate the facts surrounding the attack.
No group has claimed responsibility for the attack at the Rashidin transit point west of Aleppo. "Also at the time some of the sites where they were stored [were] besieged...and the OPCW just couldn't get to them to verify them", he says.