Britain later said that tests it conducted on samples taken from Syria also were positive for sarin.
The back-to-back announcements left many questions unanswered, highlighting the difficulties of confirming from a distance whether combatants in Syria have crossed the “red line” set by President Barack Obama. The regime of Syrian President Bashar Assad has refused to allow U.N. investigators into the country.
The French and British findings, based on samples taken from Syria, came hours after a U.N. team said it had “reasonable grounds” to suspect small-scale use of toxic chemicals in at least four attacks in March and April.
The U.N. probe was conducted from outside Syria’s borders, based on interviews with doctors and witnesses of purported attacks, and a review of amateur videos from Syria. The team said solid evidence will remain elusive until inspectors can collect samples from victims directly or from the sites of alleged attacks.
Some experts cautioned that the type of evidence currently available to investigators – videos, witness reports and physiological samples of uncertain origin – leaves wide doubts.
At the same time, forensic evidence of alleged chemical weapons use is fading away with time and the longer U.N. inspectors are kept out of Syria, the harder it will be to collect conclusive proof, they said.
Syria is suspected of having one of the world’s largest chemical weapons arsenals, including mustard and nerve gas, such as sarin. In recent weeks, the regime and those trying to topple Assad have increasingly used accusations of chemical weapons as a propaganda tool, but have offered no solid proof.
In the West, meanwhile, the lack of certainty about such allegations is linked to a high stakes political debate over whether the U.S. should get more involved in the Syria conflict, including by arming those fighting Assad.
Obama has been reluctant to send weapons to the Syrian rebels, in part because of the presence of Islamic militants among them. Obama has warned that the use of chemical weapons or their transfer to a terrorist group would cross a “red line,” hinting at forceful intervention in such an event.
Yet he has insisted on a high level of proof, including a “chain of custody” that can only come from on-site investigations currently being blocked by the regime.
In Tuesday’s announcement about sarin, French Foreign Minister Laurent Fabius said his government had analyzed several samples, including some brought back from Syria by reporters from the Le Monde newspaper.
He said that there was “no doubt” that, at least in one case, the regime and its allies were responsible for the attack. “We have integrally traced the chain, from the attack, to the moment people were killed, to when the samples were taken and analyzed,” Fabius told the TV station France 2.
He said a line was crossed and that “all options are on the table,” including intervening “militarily where the gas is produced or stored.”
In London, Britain’s Foreign Office said samples from Syria were tested at a government laboratory and the presence of sarin was confirmed. It did not say when or where the samples were obtained.