France has proof that the Syrian government launched chlorine gas attacks and has crossed a line that could prompt French airstrikes, President Emmanuel Macron said Thursday.

Macron did not specify whether France is planning military action against Syrian President Bashar Assad’s government. He said he has been talking regularly this week with U.S. President Donald Trump about the most effective response.

The U.S., France and Britain have been consulting about launching a military strike. Trump tweeted Wednesday that missiles “will be coming” and on Thursday tweeted that an attack “could be very soon or not so soon at all!”

Speaking on TF1 television, Macron said that France would not tolerate “regimes that think everything is permitted.”

He previously said any French action would target Syria’s chemical weapons abilities.

Syrian opposition activists and medics say a suspected gas attack last week in Douma killed more than 40 people. The Syrian government has denied the allegations.

Macron’s office and the French military aren’t commenting on pending plans. A military operation would be a big deal for Macron, his first military action as president, at a time of heightened domestic tensions over labor law changes.

Macron doesn’t need parliamentary permission to launch an operation.

French forces have not directly targeted Syrian government sites before, but France has supported rebel forces since early in the fighting that began in 2011.

Geopolitics specialist Dominique Moisi, a senior adviser at the Montaigne Institute?think tank in Paris, said “we have said that we were not allowing the use of chemical weapons, that this was a red line … Not to react is to prove to the rest of the world that what we say does not matter.”

Moisi stressed the “risk of escalation” of the conflict amid increasing concerns about a U.S.-Russia proxy war.

“So striking at Syria is not a good solution, but doing nothing after the use of chemical weapons is even worse,” he said.

In London, British Prime Minister Theresa May summoned her Cabinet back from vacation Thursday to discuss military action against Syria.

After meeting for more than two hours, the Cabinet gave May the green light to join the U.S. and France in planning possible strikes, but also left open the possibility of other responses.

The British leader’s office said Cabinet ministers “agreed on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime.”

Opposition lawmakers have called on May to give Parliament a vote before committing British troops. May isn’t legally required to do that, though it has become conventional since the 2003 invasion of Iraq for lawmakers to be given the chance to vote before British forces are deployed.

Chancellor Angela Merkel said after speaking with Macron on Thursday that Germany won’t participate in possible military action in Syria, but supports sending a message that the use of chemical weapons is unacceptable.

Post-World War II Germany typically has been reluctant to engage in military action, and parliamentary approval is required for any military missions abroad. The country often has restricted itself to supporting roles, such as the participation of reconnaissance jets in the international campaign against the Islamic State group.

“I think it is important to have a common line, without Germany participating militarily,” Merkel said.

France already has some 1,100 troops involved in its Operation Chammal, created in 2014 to fight Islamic State extremists in Iraq and extended in 2015 to Syria, as part of the U.S.-led coalition. Multiple Islamic State retaliatory attacks have targeted French soil, including just last month.

French warplanes operate out of French bases in Jordan and Al Dhafra in United Arab Emirates. France also has a naval base in Abu Dhabi, and an aviation center in Qatar at the U.S. air base at Al Udeid. France has 650 troops based in the United Arab Emirates overall.

In addition, a French frigate is stationed off of Lebanon in international waters.

In Syria, French warplanes carried out 23 sorties in late March and early April but fired no strikes, as part of support for Syrian opposition forces fighting in the last pockets of IS control.

(AP)