French President Emmanuel Macron waves from his car after being interviewed on French news channel TF1, at a school in Berd’huis, France, April 12, 2018. Yoan Valat/Pool via Reuters

French President Emmanuel Macron sharpened his stance Thursday on possible intervention in Syria, claiming that France has “proof” of a chemical attack last week and insisting that regimes must be held accountable for their abuses.

Macron’s comments were widely interpreted as moving France closer to joining the United States in a possible military strike despite critics’ worries about a reprise of France’s participation in a 2011 NATO intervention in Libya, which helped bring down ruler Moammar Gaddafi but left Libya in deep chaos.

Macron’s tough statement contrasted with remarks by major European partners — as well as his own assessment four months ago.

German Chancellor Angela Merkel said Thursday that her country would not join a military operation in Syria. Meanwhile, Britain has called for international chemical detection teams to visit the site of Saturday’s attack, the former rebel stronghold of Douma east of Damascus.

In December, Macron urged dialogue with the Syrian president. “We have to talk to everybody. We have to talk to Bashar al-Assad and his representatives,” he said then in a television interview. “Afterward, he must answer for his crimes before his people, before international justice.”

By Thursday, Macron appeared to have changed his tune.

“We have the proof that chemical weapons — at least chlorine gas — were used by Assad’s regime,” Macron said on France’s TF1 network as he made the case for holding the regime accountable.

Macron gave no details on France’s analysis of the attack. In Washington, Defense Secretary Jim Mattis said the United States did not have complete information about what occurred in Syria.

“I cannot tell you that we have evidence, although we certainly have a lot of media or social media indicators that either chlorine or sarin were used,” he told the House Armed Services Committee on Thursday.

Mattis said he hoped that experts from the Organization for the Prohibition of Chemical Weapons would soon be granted access to Douma, but he noted that any possible inspection would not be able to establish who was responsible for the incident.

Macron said that any military response would occur whenever it would be “most effective.” His comments echoed those of President Trump, who earlier Thursday added doubts about suggestions that a U.S. attack was on a fast track.

“Never said when an attack on Syria would take place,” Trump tweeted. “Could be very soon or not so soon at all!”

Macron has long called the use of chemical weapons in Syria a “red line” that would trigger French retaliation.

For the moment, public opinion polls in France suggest that a plurality of citizens are skeptical of carrying out a strike on Syria.

In France in particular, the memory of the 2011 Libyan operation looms especially large. In that operation — spearheaded by France’s then-president, Nicolas Sarkozy — a NATO task force conducted airstrikes that helped Libyan rebels overthrow Gaddafi but did little else to help stabilize the country.

In the years since, the public has questioned the intervention, which became a regular talking point for Sarkozy’s critics, including Macron. But France appears likely to strike Syria regardless, security analysts said.

“He’s going to do what French presidents do — which is to do it without asking anybody about it,” said François Heisbourg, a former presidential adviser on defense and national security under both Sarkozy and his successor, François Hollande. He referred to the broad powers that France’s constitution grants the executive branch.

Since the Douma attack, Macron has mostly couched his rationale as a natural response to an obvious human rights violation.

“France will not allow any escalation that could harm the stability of the region as a whole,” he said Thursday, “but we can’t let regimes think they can do everything they want, including the worst things that violate international law.”

Perhaps to address concerns over repeating the Libyan debacle, Macron also stressed in his interview that France could take on wider roles in Syria such as working with the United Nations to achieve local cease-fires and dismantling the regime’s stockpile of chemical weapons, although the details remained vague.

Much of the commentary in France over the past week has focused on whether the country could forge ahead by itself in Syria if Trump follows through on his pledge to withdraw U.S. forces from the country.

“France would have the capacity to act alone,” said Vincent Desportes, a retired general who appeared Thursday on France Info television. “Technically, it’s possible.”