UN investigators say Assad carried out sarin gas attack on Khan Sheikhoun

The report offers the strongest evidence yet that Syrian president's forces conducted the April 4 attack on Khan Sheikhoun

Syrians dig a grave on April 5, 2017 to bury the victims of the April 4 chemical attack in Khan Sheikhoun, a rebel-held town in Syria’s northwestern Idlib province. Fadi Al Halabi / AFP

The Syrian air force of President Bashar Assad was responsible for a sarin gas attack that killed at least 83 people, UN investigators said on Wednesday as they dismissed the regime’s claims that their planes had been targeting a chemical weapons site.

The attack was carried out by a Russian-built plane on the town of Khan Sheikhoun in rebel-held Idlib province on April 4 with one of the four bombs dropped containing the deadly nerve gas, according to the most recent report by the Commission of Inquiry on Syria.

The regime accepted that it had attacked the town but said the gas was released after its aircraft targeted a chemical weapons factory. UN investigators said they had found no evidence of such a site.

It was “extremely unlikely that an air strike would release sarin potentially stored inside such a structure in amounts sufficient to explain the number of casualties recorded,” the report said.

The attack on Khan Sheikhoun – which left 28 children and 23 women among the dead - prompted a retaliatory strike by the US on the airfield from where the Sukhoi-22 aeroplane took off. The plane is used only by the Syrian air force.

The report also criticised the United States for a failure to carry out sufficient checks before launching an attack on a mosque in Al Jinah, Aleppo, targeting an alleged meeting of senior Al Qaeda leaders.

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“We believe that a proper assessment of the target was not undertaken, particularly considering the target was identified three days before the attack,” the chairman of the committee Paulo Pinheiro said.

He said that target planning had only started on the day of the strike on March 16, which saw the building next to the prayer hall hit with ten bombs. A drone fired two missiles at targets who came out of the building.

Mosques are protected under international humanitarian law and must not be attacked unless they are used for military purposes, such as if an Al Qaeda meeting was being held there. The US said in June that the air strike was a valid operation that had killed about two dozen men attending a meeting of Al Qaeda fighters.

Mr Pinheiro said that investigators had not found any evidence to suggest such a meeting was taking place. Residents interviewed by the commission and first responders suggested the attack happened during a regular religious gathering.

The commission’s report said that the US targeting team “lacked an understanding of the actual target, including that it was part of a mosque where worshippers gathered to pray every Thursday”.

Mr Pinheiro said that he was gravely concerned about the impact of coalition airstrikes and called on the US to better protect civilians during air strikes on militants in the east of the country.

The committee stopped short of saying that the bombing of Al Jinah was a war crime, unlike the attack on Khan Sheikhoun strike attributed to the Syrian regime

The Khan Sheikhoun attack was just one of 33 chemical weapons attacks that it has documented. All but six have been attributed to Assad forces, with no perpetrators identified for the early attacks.

A previous investigation by chemical weapons inspectors had identified the use of sarin at Khan Sheikhoun but did not say who was responsible. Mr Pinheiro said: “It is our task to verify these allegations and we concluded… that this attack was perpetrated by the Syrian air force.”

The attack by the Syrian airforce also targeted medical facilities throughout the area, hampering attempts to treat the wounded and increasing the death toll.

The Syrian regime has continued to use sarin and chlorine gas to deadly effect throughout the war despite former US president Barack Obama describing their use as a “red line” in 2012, intimating the likely use of military action.

But following an attack on the Damascus suburb of Ghouta the following year, the US struck a deal brokered by Russia which saw the bulk of Syria’s supplies of sarin removed from the country.

The failure to attack was criticised by Donald Trump during his campaign for the presidency, and he used the attack on Khan Sheikhoun to highlight how Assad still had access to stockpiles of sarin and was prepared to use it against civilians.

The White House last month called on the international community to unite to ensure that anyone using chemical weapons faced “serious consequences” without commenting further on what those would be.

The report is the 14th by the commission and covers events from March to early July, based on interviews with Syrians, satellite images and examinations of photos and videos. It is unable to physically examine or test bomb fragments as the commission has been denied access to the territory.