But several experts have said that only the Syrian regime is likely to have stockpiles of Sarin gas. "These have tested positive for the nerve agent sarin, or a sarin-like substance", the delegation said during a special session at the Organisation for the Prohibition of Chemical Weapons in The Hague. "Even if we have them, we wouldn't use them, and we have never used our chemical arsenal in our history".

The Syrian army meanwhile issued a statement saying that the US -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.

Since September 2015 Russian Aerospace Forces have been carrying out airstrikes in Syria targeted at terrorist positions at the request of Syrian President Bashar Assad.

Earlier testing by Turkish authorities had also said the chemical used on April 4 was sarin.

Senior administration officials "suggested that the attack may have been motivated by rebel gains in the surrounding area, as rebel forces approached a strategic Syrian air base", NPR's Scott Horsley reports.

Other world powers have also condemned Assad for the April 4 attack - although Syrian ally Russian Federation continues to maintain there is insufficient evidence Assad carried out the attack.

After the voting, Russia's Deputy Permanent Representative to the United Nations Vladimir Safronkov said that had the draft resolution been adopted, it would have justified the U.S. missile attack on Syria which actually had been a violation of global law.

At the same time, Assad pointed out that the Syrian army's military capabilities had not been affected.

In an exclusive video interview with the Agence France-Presse (AFP) news agancy, Mr Assad said "there was no order to make any attack". "Were they dead at all?", he said.

Government ally Russian Federation on Wednesday vetoed a draft UN Security Council resolution demanding Syria co-operate with an worldwide investigation of the attack. "We don't know whether those dead children were killed in Khan Sheikhoun, were they dead at all?" he said. Its findings, expected in 3-4 weeks, will be passed to a joint United Nations-OPCW investigation tasked with identifying individuals or institutions responsible for using chemical weapons.

"India is a signatory to the chemical weapons convention".

It said Mansour admitted to fighting against Lebanese troops in northern Lebanon in the past and was involved in smuggling weapons to the al-Qaida-linked Nusra Front in Syria, now known as the Fatah al-Sham Front.

The report says the USA relied on "signals intelligence and geospatial intelligence, laboratory analysis of physiological samples collected from multiple victims, as well as a significant body of credible open source reporting".

When specifically asked about the air strikes by the United States, he said "I have referred to the meeting of the USA and Russian foreign ministers".

Assad said he would only allow an "impartial" external investigation involving "unbiased countries", according to AFP.