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PARIS, June 30 (Reuters) - France said on Friday that a report by the world's chemical weapons watchdog that nerve agent sarin was used in an April attack in Syria was "unequivocal" and that the organisation's members should act firmly on its findings.
After interviewing witnesses and examining samples, a fact- finding mission (FFM) of the Organisation for the Prohibition of Chemical Weapons (OPCW) concluded that "a large number of people, some of whom died, were exposed to sarin or a sarin-like substance.
"The conclusions of this report are indisputable," the foreign ministry said in a statement.
"The OPCW and its members must assume their responsibilities and condemn, in the strongest terms, this intolerable violation of the non-proliferation regime."
The attack on April 4, when dozens of people were killed in the town of Khan Sheikhoun in northern Idlib province, was the most deadly in Syria's civil war in more than three years.
A joint United Nations and OPCW investigation, known as the JIM, can now look at the incident to determine who is to blame.
Western intelligence agencies have accused the government of Bashar al-Assad of carrying out the attack. Syrian officials have repeatedly denied using banned toxins in the conflict.
Russia, Assad's key backer, said on Friday the OPCW's findings were based on doubtful evidence.
France, under President Emmanuel Macron, has been pushing for closer cooperation with Moscow, especially over Syria, and has said dialogue with Russia on enforcing a 2013 Security Council resolution to prevent the use of chemical weapons in Syria was one of its priorities.
The Khan Sheikhoun attack prompted a U.S. missile strike against a Syrian air base which Washington said was used to launch the strike. France has said any new attacks would be a "red line" that could see unilateral French air strikes.
"Those who carried out the Khan Sheikhoun atrocities and other chemical weapons attacks must face justice for the crimes," the ministry said. (Reporting by John Irish; Editing by Bate Felix and Ralph Boulton)