(CNN) -- Sarin gas has been used several times in the Syrian civil war, including at least once by the Assad regime, France's foreign minister said Tuesday, citing results from test samples in France's possession.
Laurent Fabius announced that conclusion after meeting with the head of a United Nations mission set up to establish the facts about the alleged use of chemical weapons in Syria.
"I gave him the results of tests carried out by our lab appointed by the Organization for the Prohibition of Chemical Weapons to identify chemical warfare," Fabius said in a statement, referring to the Swedish scientist Professor Ake Sellstrom.
"These results show the presence of sarin in the samples that are in our possession," Fabius said. "In view of these elements, France now has the certainty that the sarin gas was used in Syria several times and in a localized manner."
In an interview later Tuesday with CNN affiliate France 2, Fabius blamed the Syrian government in at least one of the cases.
"There is no doubt that it is the regime and its accomplices," Fabius said. He added the French government examined the chain of events from the moment of the attack through the lab results to determine that government was responsible.
Fabius' announcement did not say when or where the weapons may have been used or who may have used the gas in the other cases.
Syrian rebels have been fighting the government for more than two years. Atrocities have been blamed on both sides.
The announcement coincided with the release of a draft report posted on the website of the U.N. Human Rights Council that concludes: "There are reasonable grounds to believe that chemical agents have been used as weapons. The precise agents, delivery systems or perpetrators could not be identified."
In Washington, White House press secretary Jay Carney said the United States was working with the French and other allies as well as the Syrian opposition to determine those answers.
"We need to expand the evidence we have," he told reporters Tuesday. "We need to make it reviewable; we need to have it corroborated before we make any decisions based on the clear violation that use of chemical weapons would represent by the Syrian regime. So, we will continue in that effort."
Asked how long that might take, he said, "I don't have a timetable for you."
He noted that Damascus has consistently turned down U.S. requests for a U.N. investigative team to be sent to Syria.
"But we are not relying on the United Nations alone," he said. "We are aggressively pursuing other avenues to gather the evidence that is required."
Earlier this year, the United States said its intelligence analysts had concluded "with varying degrees of confidence" that chemical weapons had been used in Syria. But President Barack Obama said "intelligence assessments alone are not sufficient."
In early May, the head of the U.N. Independent International Commission of Inquiry on Syria said that evidence points to the use of sarin by Syrian rebel forces. But the commission later issued a news release saying it "has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict."
In April, the head of the Israeli military's intelligence research said the Syrian government is using chemical weapons against rebel forces.