President Emmanuel Macron said Tuesday that "France will strike" if chemical weapons are used against civilians in the Syrian conflict in violation of international treaties, but that he had not yet seen proof this was the case.

Macron said last May that the use of chemical weapons would represent a "red line." In a telephone call Friday with Russian President Vladimir Putin he expressed concern over signs that chlorine bombs had been used against civilians in Syria.

"On chemical weapons, I set a red line and I reaffirm that red line," Macron told reporters. "If we have proven evidence that chemical weapons proscribed in treaties are used, we will strike the place where they are made."