BEIRUT -- The deadly nerve agent sarin was used in an attack that killed scores of civilians in northern Syria this month, the global chemical weapons watchdog said Wednesday.

The attack, which the Trump administration has attributed to the Syrian government, elicited horror across Western capitals and prompted the United States to launch its first military action against Syrian President Bashar al-Assad, six years into a war in which atrocities against civilians have become a daily occurrence.

The Organization for the Prohibition of Chemical Weapons (OPCW) said Wednesday that samples from 10 separate victims of the attack indicated exposure to sarin or a sarin-like substance.

"While further details of the laboratory analyses will follow, the analytical results already obtained are incontrovertible," said Ahmet Üzümcü, the organization's director-general.

The attack in the northwestern town of Khan Sheikhoun woke hundreds of civilians in the early hours of April 4. Within minutes, many were choking and in convulsions on the ground. Others had already died in their sleep.

At least 86 people were killed and more than 500 others affected, according to monitoring groups and local doctors.

International conventions prohibit the use of sarin, which turns a victim's nervous system against them and can kill within seconds. On April 4, survivors said they felt as if their lungs were on fire.

Assad's government denies using chemical weapons against its own people, despite its involvement in a 2013 sarin attack which is believed to have killed more than 1,000 residents of the rebel-held Damascus suburbs.

On Wednesday, France said it would soon provide proof of the Syrian regime's involvement in the latest attack as well.

"There is an investigation underway (by) the French intelligence services and military intelligence . . . it's a question of days and we will provide proof that the regime carried out these strikes," said French Foreign Minister Jean-Marc Ayrault.

"We have elements that will enable us to show that the regime knowingly used chemical weapons," he added.