This means that French President Emmanuel Macron will keep one of the promises in his election campaign.
He added that while the priority is still to fight the remains of ISIS and jihadist terrorism in Syria, the Assad regime will not escape justice.
Macron, in a meeting with the Presidential Press Association, reiterated his threat of several months ago to take "unilateral" military action against the Syrian army and warned of a "riposte" if it is proven that chemical weapons are still being used in that conflict.
At the same time, he added, that "today our services have not established proof that proscribed chemical weapons have been used against civilian populations". Both Syrian President Bashar al-Assad and his ally Russian President Vladimir Putin have said that attack was fabricated and that a conventional airstrike hit a rebel cache of chemical weapons. He added that is such proof is found, France will strike the places from where the shipments of chemical weapons are originating.
While France, like the United States, suspects the Syrian regime, it says it does not yet have concrete evidence on the nature and origin of the attacks.
Macron, who has pushed both the USA and France to take a more active role in Syria, echoed Mattis' language in his remarks Tuesday.
In a sign of cabinet tensions, Florence Parly, the defence minister, said the new national service could not be made obligatory, but she was contradicted by Gérard Collomb, the interior minister. "So we, alongside the others, are working on trying to confirm this, as we clearly have to get the facts straight".
Syria signed the global treaty banning chemical weapons and allowed monitors to destroy its poison gas arsenal after an agreement reached in 2013 to avert U.S. retaliation for what Washington said was a nerve gas attack near Damascus that killed more than 1,000 people.