France deployed nine jet fighters and five frigates and fired 12 cruise missiles during the air strikes, which were US-led with Britain also taking part.
"The targets that were set have been hit," Le Drian told BFMTV on Saturday, warning that if Paris believes the "red line" is crossed again, more strikes will take place.
"But I think the lesson will have been understood," he added.
French report declassified
Shortly after the overnight attack, the French government declassified a report on the 7 April attack on Douma, in the former rebel stronghold of Eastern Ghouta, as evidence that Assad's forces used chemical weapons there.
The conclusion is based on "reliable intelligence" and videos and images posted on social media.
It cited NGOs, naming the Syrian American Medical Society and the Union of Medical Care and Relief Organisations, "whose information is generally reliable", as saying that strikes particularly targeted local medical infrastructure on 6-7 April.
"A massive influx of patients in health centres in Eastern Ghouta (at the very least 100 people) presenting symptoms consistent with exposure to a chemical agent was observed and documented during the early evening, the report says, adding that several dozen people are thought to have died from exposure to a chemical substance.
Agents examined images and videos published online and identified symptoms, including suffocation and breathing difficulties, hpersalivation and hypersecretions, cyanosis (discolouration of the skin or mucous membranes), skin burns and corneal burns.
"They were able to conclude with a high degree of confidence that the vast majority are recent and not fabricated," the report said.
Why would Assad use chemical weapons?
The French argue that it was in Assad's interests to launch the attack because between 4,500 and 5,500 fighters from the Islamist group Jaysh al-Islam had refused to accept a surrender agreement with the Syrian and Russian governments that had been accepted by other rebels.
Russian military forces in Syria allow the Assad government air superiority, "giving it the total military freedom of action it needs for its indiscriminate offensives on urban areas", the report states.
"Given this context, the Syrian regime’s use of chemical weapons makes sense from both the military and strategic points of view," it says.
France claims that the Assad government never declared all its stockpiles of chemical weapons after "its late, half-hearted accession to the Chemical Weapons Convention (CWC) in October 2013" and has continued a clandestine chemical weapons programme.
" A considerable increase in chlorine attacks since the beginning of the offensive on Eastern Ghouta has also been clearly observed and proven," the report says, insisting that "Damascus seeks to seize a tactical military advantage locally, and above all to terrorise populations in order to break down all remaining resistance."
It concedes that French laboratories have not analysed chemical samples but concludes "(i) that, beyond possible doubt, a chemical attack was carried out against civilians at Douma on 7 April 2018; and (ii) that there is no plausible scenario other than that of an attack by Syrian armed forces as part of a wider offensive in the Eastern Ghouta enclave."
Russia rejects charges
Russia slammed the report, casting doubt on social media as viable sources.
"The pretext for the attack, according to the statements made by US officials and the so called secret report recently published by French intelligence agencies, were mass media and social media publications," Russian foreign ministry spokeswoman Maria Zakharova said.
Moscow on Saturday said it remained in contact with Washington, London and Paris, despite the air strikes.