Samples taken from the poison gas site in Syria's Idlib governorate tested positive for the nerve agent sarin, the British delegation at the OPCW said on Thursday.

In Moscow, Russian Foreign Minister Sergey Lavrov said Thursday that OPCW inspectors should visit both the Syrian air base, which the US said served as a platform for the attack, and Khan Sheikhoun to get a full and objective picture.

Britain's Ambassador, Sir Geoffrey Adams, told the meeting that United Kingdom scientists have analyzed samples from Khan Shaykhun and they "tested positive for the nerve agent sarin, or a sarin-like substance".

Dozens of children were among those killed in one of the deadliest gas attacks in the six-year civil war. Meanwhile, sources talking to Reuters said that OPCW investigators have gone to Turkey to collect samples as part of an inquiry into the alleged chemical weapons. The National Coalition for Syrian Revolutionary and Opposition Forces earlier on April 4 said some 80 people were killed and 200 injured in a chemical weapons attack in Khan Shaykhun in the Idlib province, and blamed the Syrian army for the incident.

US ambassador Ward insisted it was a deliberate attack that amounted to "a direct affront to the Chemical Weapons Convention and, indeed, a direct affront to human decency, carried out by a State Party" to the OPCW, according to the text of his speech that was posted on the organization's website. On April 6, Donald Trump authorized retaliatory strikes against Syrian military targets.

American officials reportedly see the hospital bombing as an attempt to cover up the use of chemical weapons. But Assad also refuted these claims, claiming that it had not been affected by the attack.

"On April 4, the lifeless bodies of innocent victims, grotesquely contorted and twisted by the nerve agent sarin, tell the real story", Ward said.

In his AFP interview, Assad accused the West, particularly the United States, of being "hand-in-glove with the terrorists" over the Khan Sheikhoun incident. Graphic footage showed men, women and children gasping for breath, foaming at the mouth and convulsing. "You have a lot of fake videos now". We don't know if they were dead or who committed the attack. He said Khan Sheikhun had no strategic value and was not now a battle front.

On Wednesday, Russia vetoed a United Nations resolution condemning the reported use of chemical weapons, which would have prompted an investigation into the deaths in Khan Sheikhoun.

Assad said no proper investigation had been possible because the area was controlled by Nusra Front. Al-Assad said more USA attacks "could happen anytime, anywhere, not only in Syria".

"We are deeply anxious by our partners in the U.N. Security Council trying to evade an honest investigation into that episode", he said. Meanwhile, the Syrian army said an air strike late on April 12 by the US -led coalition hit poison gas supplies belonging to the Islamic State of Iraq and the Levant (ISIL), releasing a toxic substance that killed "hundreds", but the coalition denied carrying out raids in the area.

Syrian authorities have repeatedly denied using any chemical weapons. U.S. Air Force Colonel John Dorrian, a spokesman for the coalition, said it had carried out no air strikes in that area at that time. The report could not immediately be independently verified.