A report by the international chemical weapons watchdog has confirmed that the banned nerve agent Sarin gas was used in the deadly attack in Northern Syria on April 4, Reuters reported on Friday. While the report by the Organisation for the Prohibition of Chemical Weapons did not accuse any entity of being responsible for the strike, a joint United Nations-OPCW investigation will be conducted.

“It is the conclusion of the fact-finding mission that such a release can only be determined as the use of sarin as a chemical weapon,” the report said.

OPCW Director-General Ahmet Uzumcu “strongly condemned this atrocity”, which he said “wholly contradicts the norms enshrined in the Chemical Weapons Convention”. “The perpetrators of this horrific attack must be held accountable for their crimes.”

The United States and the watchdog defended the team’s decision against visiting the site to conduct the investigation, citing security reasons. The team analysed samples from victims and survivors and also interviewed witnesses, AP reported.

The attack in Idlib province’s Khan Sheikhoun is believed to have killed more than 90 people and injured many more. On April 7, the US military had carried out targeted missile strikes on a Syrian base as a “response” to the suspected chemical attack. The Syrian Army had said the strike had killed six troops and caused “big material losses”. In his statement after the strikes, US President Donald Trump had said the suspected gas attack had “cross a lot of lines” for him.

On April 25, the US had blacklisted 271 Syrian chemists and employees of a government research centre as punishment for the country’s alleged role in the attack. The next day, a declassified French intelligence report had said forces allied with Syrian President Bashar al-Assad had carried out the sarin gas attack, and that Assad or his aides had ordered the strike. The Syrian leader had refuted the allegations.

In September 2016, the Syrian government was accused of dropping barrel bombs containing chlorine in the Sukari area of Aleppo. More than 80 civilians were killed in the incident.