“France will strike” if chemical weapons are found to have been used against civilians in the Syrian conflict in violation of international treaties, French President Emmanuel Macron has warned.

Macron delivered the warning in a telephone call with Russian President Vladimir Putin. In it he expressed concern over signs that chlorine bombs had been used against civilians in Syria and it follows his public promise last May that the use of chemical weapons would represent a “red line.” Reuters reports he said:

On chemical weapons, I set a red line and I reaffirm that red line. If we have proven evidence that chemical weapons proscribed in treaties are used, we will strike the place where they are made. Today, our agencies, our armed forces have not established that chemical weapons, as set out in treaties, have been used against the civilian population.

The Syrian government has repeatedly denied using chemical weapons and said it targets only armed rebels and militants, although plenty of allegations have been made during the bloody Syria civil war. This is despite the fact Russia guaranteed that Damascus destroyed its entire chemical weapons arsenal in 2014.

As Breitbart News reported, as recently as last month rescue workers were reporting that warplanes from the regime of Syria’s president Bashar al-Assad and from his ally Russia had stepped up bombing attacks on civilians in densely populated neighborhoods in Eastern Ghouta and Idlib, and the use of chlorine gas was reported. At least 29 people were killed.

Typically, chlorine gas is delivered through the use of barrel bombs. The barrel bombs are filled with metal and chlorine gas in order to maximise casualties.

Last week the State Department and U.S. Ambassador to the United Nations Nikki Haley condemned the Russian government following those reports of Syrian government attacks on civilians using chemical weapons.

Ambassador Haley also made remarks condemning a Russian draft resolution at the U.N. Security Council intended to address the chemical weapons issue.

“For their new investigation, Russia wants to be able to cherry pick the investigators. It wants to insert unnecessary and arbitrary investigative standards,” she said. “And it wants the Security Council to be able to review all of the findings of this investigation and decide what makes it into the final report. This is not an impartial mechanism. It is a way to whitewash the findings of the last investigation that Russia desperately wants to bury.”

“Few things have horrified my country and the world as much as the Assad regime’s use of chemical weapons against its people. This Council has been outspoken on ending Syria’s use of chemical weapons, and yet, they continue,” Haley noted.

France and the United Nations have repeatedly called in past months for a Syria ceasefire and the opening of aid corridors to alleviate the region’s humanitarian crisis. Russia, Assad’s most powerful ally, said last week a ceasefire was not realistic.