The Bashar al-Assad government authorised the deadly nerve gas attack in northern Syria earlier this month, according to French intelligence.
Scores of people were killed in the chemical weapons attack on the town of Khan Sheikhoun, which a declassified report claims bears the signature of the regime.
The six-page document drawn up by France's military and foreign intelligence services analysed samples from the impact and blood from a victim.
"We know, from a certain source, that the process of fabrication of the samples taken is typical of the method developed in Syrian laboratories," Foreign Minister Jean-Marc Ayrault told reporters.
"This method is the signature of the regime and it is what enables us to establish the responsibility of the attack."
Assad or members of his inner circle ordered the strike, the report shows.
In two interviews since April 4, the Syrian President has said evidence of a poison gas attack was false and denied his government had ever used chemical weapons.
The attack prompted the US to launch a cruise missile strike on a Syrian air base, its first deliberate assault on the Assad government in the six-year-old conflict.
