The United States is evaluating information received from France which Paris has billed as proof that chemical weapons have been used in Syria, a US official said Thursday.

"I can confirm for you that we have received the information from the French," State Department spokeswoman Jen Psaki told reporters, after French officials said they had evidence that sarin gas had been used in Syria.

"We will take a close look at this, just like we take a close look at any information that's provided, and we always recommend that any country provide information as well to the UN for their full investigation."

But Psaki warned the US did not intend to "evaluate or litigate in public" whatever information it has received from Paris.

"We are still looking into finalizing the facts, looking into confirming the facts," she said, denying that the close inspection of the French information was pouring doubt on its credibility.

"We're doing our own due diligence on this," Psaki stressed.

President Barack Obama has said that any use of chemical weapons in the Syria conflict, now in its third year, would violate a US "red line". But amid mounting reports such arms have been used, Washington has proceeded cautiously.

Amid mounting pressure for the US to act, Secretary of State John Kerry called on France on Wednesday to share its 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.

France has described the evidence of sarin use as a development that obliges the international community to act.

But memories remain strong in the United States about the false evidence that former Iraqi leader Saddam Hussein had stockpiled chemical weapons, which was used to justify the 2003 US invasion of Iraq.