Turkey urged the United Nations Security Council on Friday to take “concrete action” after an alleged chemical weapons attack in neighboring Syria, a day after France’s foreign minister Laurent Fabius had called on the world to respond with “force.”

Fabius immediately cautioned against “sending troops” in an interview with BFM television but France has repeatedly called for intervention in Syria’s civil war through the last three years, suggesting, like Turkey, that “humanitarian corridors” be erected to deliver food and medicine to victims of the conflict.

Syrian opposition activists accused the regime of President Bashar Assad of gassing hundreds of civilians on Wednesday. Amateur videos purporting to show victims of the attack were published online. Neither foreign journalists nor independent observers were able to corroborate the claim.

Previous accusations of chemical weapons use could not be decidedly proven either. In April, American officials said they believed with “varying degrees of confidence” that sarin had been used by Assad’s army. However, they noted that “the chain of custody is not clear,” suggesting that an order to deploy the gas might not have come from the top.

There is also the possibility that nerve gas was used by rebels emboldened by American president Barack Obama’s insistence one year ago that the use of such weapons would cross a “red line.” While he failed to explain why or what action the United States would take if chemical weapons were used, his administration did announce in June that it would start providing opposition fighters with small arms.

The United States were previously reluctant to arm rebel fighters for fear of propping up a jihadist insurgency. Most of the communications equipment and weapons supplied by the United States and its allies in the region, including Qatar, Saudi Arabia and Turkey, have ended up in the hands of religious extremists who now appear the most effective fighting force in the opposition.

The timing of this week’s alleged gas attack raises more doubts. On Sunday, United Nations inspectors arrived in Syria to investigate previous allegations of chemical weapons use. Would the regime deploy nerve gas, close the capital Damascus moreover, less than three days after letting international monitors into the country?

Turkey and the United Kingdom were certain it did. Prime Minister Recep Tayyip Erdoğan said in a television interview late on Thursday that it was “very obvious” chemical weapons had been used. “It is now time for actual concrete action,” President Abdullah Gül told reporters the next day when Britain’s foreign secretary William Hague argued that the chances of the Syrian opposition having deployed the gas were “vanishingly small. And so we do believe that this is a chemical attack by the Assad regime.”