The Associated Press reports: Samples taken from Syria and tested in France have confirmed that sarin gas has been used there multiple times, France’s foreign minister said Tuesday.

Laurent Fabius said the tests carried out by a French laboratory “prove the presence of sarin in the samples in our possession.” He said France “now is certain that sarin gas was used in Syria multiple times and in a localized way.”

The brief statement concluded: “It would be unacceptable that those guilty of these crimes benefit from impunity.”

Earlier Tuesday, a U.N. report on Syria said there are “reasonable grounds” to believe that limited quantities of toxic chemicals have been used as weapons in at least four attacks in Syria’s civil war, but that more evidence is needed to determine the precise chemical agents used or who used them.

The U.N. Commission of Inquiry said conclusive findings can be reached only after testing samples taken directly from victims or the site of the alleged attacks. It called on Damascus to allow a team of experts into the country, saying lack of access continues to hamper the commission’s ability to fulfill its mandate.