French President Emmanuel Macron said on Thursday he has proof that the Bashar al-Assad regime in Syria had used chemical weapons in the attack in suburban Damascus on Saturday.

“We have proof that chemical weapons were used last week, at least chlorine, and that they were used by the regime of Bashar al-Assad,” he said during an interview on France’s TF1 television, according to AFP.

Macron said he was contact with United States President Donald Trump every day and the two would decide on their response to the suspected chemical attack in the rebel-held Douma town “at a time of our choosing, when we judge it to be the most useful and the most effective”.

Rescue workers said at least 70 people were killed in the attack, but the toll will rise as they get access to the basements where civilians sought refuge from the attack. They added that many of the injured showed symptoms indicating that they were exposed to a compound containing nerve gas.

“France will in no way allow an escalation or anything that would harm regional stability, but we cannot allow regimes believe they can act with impunity to violate international law in the worst possible way,” the French president said during the interview.

Meanwhile, Trump tweeted a clarification saying he had never said when the US would attack Syria. “Could be very soon or not so soon at all!” he said on Twitter. “In any event, the United States, under my administration, has done a great job of ridding the region of ISIS. Where is our ‘Thank you America?’”

It was reported on Tuesday that Trump was expected to make a decision by that evening on the action the US military will take against the suspected chemical attack in Syria. While it was unclear how the US would make Syria and its allies “pay a price” for civilian deaths, Trump’s statement indicated that he held Russian President Vladimir Putin responsible for the attack for his association with Syria. Trump is assumed to have close ties with Putin.

Both Syria and Russia, its biggest supporter, have denied involvement in the attack, instead claiming that rebel groups had fabricated it to thwart the advances of Syrian troops and provoke global military intervention.

On Thursday, after the US and France made statements, Moscow urged the West to “seriously consider” the consequences of threatening Syria with retaliation for the alleged chemical attack, AFP reported.

“We call upon...members of the international community to seriously consider the possible consequences of such accusations, threats and especially action [against Syria],” said Maria Zakharova, spokesperson for Russia’s Ministry of Foreign Affairs. “Nobody has authorised Western leaders to take on the role of the global police.”