A global chemical weapons watchdog has concluded that sarin gas was used in an attack in Syria in April which killed more than 90 people.

The Organisation for the Prohibition of Chemical Weapons (OPCW) says people were exposed to a chemical weapon on April 4th 2017 in the Khan Shaykhun area of Idlib province.

The group was asked is to determine whether chemical weapons or toxic chemicals as weapons have been used in Syria.

However, the group said it was not asked to identify who is responsible for alleged attacks.

The OPCW said a team deployed within 24 hours of being alerted to the incident.

But for security reasons, it was unable to visit Khan Shaykhun.

"The rapid deployment to a neighbouring country, however, enabled the team to attend autopsies, collect bio-medical samples from casualties and fatalities, interview witnesses and receive environmental samples", it said.

The results of the fact-finding mission report have been shared with states who belong to the Chemical Weapons Convention, the OPCW’s Executive Council and the United Nations Security Council.

They will consider the findings at an executive council meeting on July 5th.

Photos released by the Pentagon show the location of the alleged chemical weapons attack in Khan Shaykhun, Syria | Image: USA TODAY Network/SIPA USA/PA Images

The OPCW Director-General Ahmet Üzümcü said: "I strongly condemn this atrocity, which wholly contradicts the norms enshrined in the Chemical Weapons Convention.

"The perpetrators of this horrific attack must be held accountable for their crimes.

"In this context, the work of the Joint Investigative Mechanism assumes high importance."

The US envoy to the United Nations, Nikki Haley, said in a statement: "Now that we know the undeniable truth, we look forward to an independent investigation to confirm exactly who was responsible for these brutal attacks so we can find justice for the victims."

The attack caused an international uproar, with photos seen around the world of children struggling for breath and dying.

US President Donald Trump cited the attack when he launched an airstrike on Syria a few days later, firing cruise missiles on a Syrian air base from where the US said the attack had been launched.

Syria's President Bashar al Assad has denied responsibility for the attack.

When the Syrian government joined the OPCW in 2013, after it was blamed for a poison gas attack in Damascus, it declared around 1,300 tons of chemical weapons which were later destroyed.

But there have been doubts raised over whether the country's initial declaration was true.

Additional reporting: IRN