"There is no doubt that it's the regime and its accomplices," he told France 2 television. "It would be unacceptable that those guilty of these crimes remain unpunished."
Both France and Britain have pushed to be allowed to arm several rebel groups and have used the suggestion that chemical weapons are being used by the regime as an argument in their favour.
Last week, the European Union lifted its embargo on supplying weapons to Syria, opening up the possibility both countries could now legally supply opposition groups.
Britain's Foreign Secretary, William Hague, said that before any such decision was taken, a peace conference, planned for this month, should be given an opportunity to find a political resolution to the crisis.
United States President Barack Obama called in April for a "vigorous investigation", saying the use of such weapons would be a "game changer" if verified.
The French findings come just hours after a UN report into human rights abuses in the bloody civil war. The report suggested both sides - government troops loyal to President Bashar al-Assad and a number of the various rebel groups - were responsible for using chemical weapons.
The report found "reasonable grounds" to believe chemical weapons had been used on four occasions in March and April but could not determine by which side.
"There are reasonable grounds to believe that limited quantities of toxic chemicals were used. It has not been possible, on the evidence available, to determine the precise chemical agents used, their delivery systems or the perpetrator," said Paulo Pinheiro, who chairs the UN inquiry.
The brutality of the civil war shows no sign of abating with murder, rape, summary execution and hostage taking, perpetrated by both sides, increasingly commonplace, says the UN Human Rights Council.
A council report warns that without a political solution to the crisis the gross violations of human rights it has documented will continue, and also worsen with the greater proliferation of arms in the country.
Saying both sides in the now two-year-long civil war are guilty of war crimes, the UN body says forces loyal to Assad "have committed murder, torture, rape, forcible displacement, enforced disappearance and other inhumane acts. Many of these crimes were perpetrated as part of widespread or systematic attacks against civilian populations and constitute crimes against humanity."
The myriad rebel groups - all fighting for Assad's ouster, but some secularist, others Islamist - have also committed war crimes, says the report, but the violations - which include murder, summary execution, kidnapping and pillage - "did not, however, reach the intensity and scale of those committed by government forces and affiliated militia".
The UN report covers the period between January 15 and May 15, during which time the authors say "war crimes and crimes against humanity have become a daily reality in Syria where the harrowing accounts of victims have seared themselves on our conscience".
An estimated 80,000 people - including thousands of civilians - have been killed during the war, which has also driven more than a million overseas to avoid the fighting.
Many analysts consider the conflict a proxy for wider tensions in the Middle East, with the Assad regime being supported by Shia Iran and many of the rebel groups receiving assistance from countries such as Qatar and Saudi Arabia.
But outside support for both sides has led to a quagmire which has prevented either side from gaining the necessary military advantage to win the war.
At the same time, grave human rights abuses, and a complete gambit of war crimes, have filled the resulting vacuum.
A deadly drop
• Sarin gas is a nerve agent invented by German scientists as part of Hitler's preparations for World War II.
• It is 20 times more deadly than cyanide. A drop the size of a pinhead can kill a person.
• Known as the poor man's atomic bomb as a small amount can kill a lot of people.
• Kills by crippling the nervous system through blocking the action of an enzyme.
• Can only be manufactured in a laboratory.
- Independent
