United Kingdom analysis of samples from the Syria chemical attack has detected sarin or a sarin-like substance, Britain's UN ambassador has said.
The White House report, however, cited "a wide body of open-source material" and "social media accounts" from the area occupied by foreign-backed militants in the country, including footage provided by the White Helmets rescue group, which has been documented to have ties with anti-Damascus militant groups as well as Western and Persian Gulf Arab governments backing the overthrow of Syrian President Bashar al-Assad.
The OPCW's executive council held a session of its executive council on Thursday to address the attack on Khan Sheikhoun, in the rebel-held province of Idlib, northern Syria.
Assad insisted it was "not clear whether it happened or not, because how can you verify a video?". The Assad government used chlorine in the past, while ISIS terrorists attacked with sarin and mustard gas. The Britain-based Syrian Observatory for Human Rights said 25 SDF fighters were killed in the last two days of battle.
"Our firepower, our ability to attack the terrorists hasn't been affected by this strike", he said.
Assad said he would only allow an "impartial" external investigation of last week's suspected chemical attack.
It's not immediately clear who will succeed her in leading the joint investigative initiative by the United Nations and the Organization for the Prohibition of Chemical Weapons to assess blame for chemical attacks.More news: These Rangers Hab to learn how to win playoff games at Garden
The toxic gas attack on April 4, which killed scores of children, prompted the United States to launch missile strikes on a Syrian air base and widened a rift between the United States and Russian Federation, a close Syrian ally.
The resolution would have demanded the Syrian government cooperate with an investigation into the chemical attack in the rebel-held town of Khan Sheikhun.
On Tuesday, similar results were confirmed by Turkish health officials who said post-mortem tests on victims of the suspected attack concluded that the deadly sarin nerve agent had been used.
Matthew Rycroft told the Security Council: "The United Kingdom therefore shares the U.S. assessment that it is highly likely that the regime was responsible for a sarin attack on Khan Sheikhoun on 4 April".
The Syrian army meanwhile issued a statement saying that the USA -led coalition attacked a position of the Islamic State group in the eastern province of Deir el-Zour, killing hundreds of fighters and civilians, many of them from poisonous gas.
The mission will determine whether chemical weapons were used, but is not mandated to assign blame.
Investigators determined in the past that during Syria's civil war, sarin, chlorine and mustard gas were used.