Le Drian said international law “is being violated by Turkey, by the Damascus regime, by Iran and those who are attacking eastern Ghouta and Idlib”. His remarks amount to France’s toughest line yet on Turkey’s involvement in the Syrian conflict.

Le Drian is due in Tehran on March 5 for talks over its ballistic missile program, the nuclear deal agreed with world powers in 2015 and the role of Iran in the region at a time when the United States has put pressure on its European allies to toughen their stance on Tehran.

Relations between France and Iran have deteriorated in recent months, with the sides repeatedly exchanging barbs. Le Drian has accused Iran of harboring “hegemonic” aspirations in the region.

Iran is a key ally of the Syrian government in the seven-year civil war and it says it has no intention of withdrawing unless Syria requested it do so.

Le Drian also said it looked likely that President Bashar al-Assad’s forces were using chlorine gas in their Russian-backed offensive on the rebel-held Idlib province and in the besieged enclave of eastern Ghouta.

“I‘m speaking with a degree of caution because you have to be careful pending full documentation, but all the indications that we have show that at the moment chlorine is being used by the Syrian regime,” Le Drian said, adding that the United Nations had opened an investigation.

French President Emmanuel Macron said in May last year that he had clear red lines on chemical weapons saying that “any use of chemical weapons would result in reprisals and an immediate riposte, at least where France is concerned.”