France has sent the United States "all the information it has" on what it has billed as proof that chemical weapons have been used in Syria, a foreign ministry spokesman said on Thursday.
The move follows a request on Wednesday from US Secretary of State John Kerry amid mounting pressure for the United States administration to act in response to the evidence of chemical weapons use.
French Foreign Minister Laurent Fabius personally called Kerry on Monday and informed him that all the information at France's disposal would be transmitted to Washington, ministry spokesman Philippe Lalliot told reporters.
"That has since been done by the relative services as well as by diplomatic channels," he added.
US officials have appeared to be playing down the significance of France's assertion that it is now "certain" that the Syrian regime had used the deadly nerve agent sarin in at least one attack.
Kerry said Wednesday he wanted to see "information that shows us the chain of custody of that evidence, so we know precisely where it came from."
France has described the evidence of sarin use as a development that obliges the international community to act but Washington has been reluctant to confirm a perceived violation of its own "red line" against the Syrian regime's use or movement of chemical weapons.