French Foreign Minister Jean-Marc Ayrault
French Foreign Minister Jean-Marc AyraultReuters

France on Thursday expressed alarm at reports of a deadly chemical attack a day earlier in the Syrian battleground city of Aleppo, AFP reported.

Foreign Minister Jean-Marc Ayrault said in a statement he was "concerned by reports of a new chemical attack... that is said to have claimed four lives people and left dozens injured."

"I strongly condemn all attacks on the civilian population, particularly those in which chemical weapons are used," he added.

Asked about the reported attack Thursday during a news conference in Geneva, the UN envoy to Syria, Staffan de Mistura, said it was not in his remit to verify such reports but that "there is a lot of evidence that it actually did take place".

"If it did take place, it is a war crime and as such it would require everyone... to address it immediately," he added, according to AFP.

In the past two years there have been numerous allegations of chemical weapons being used against civilians, both by President Bashar Al-Assad's regime and the rebels trying to oust him.

The United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) are due to report later this month on their investigation into nine chemical weapons attacks in 2014 and 2015.

Ayrault said he would be "particularly attentive" to their findings.

In January, the OPCW announced that all of Syria's declared chemical arms stockpile had been completely destroyed, part of a 2013 deal under which Syria agreed to destroy its chemical weapons arsenal. Since then, however, the OPCW has found that chlorine has been "systematically and repeatedly" used as a weapon.

Just last week, the defense ministry of Russia, a staunch ally of Assad, accused rebels in Aleppo of killing seven people in an attack using a "poisonous agent".

The Russian claim came on the heels of reports that two dozen people had suffered breathing difficulties in the rebel-held town of Saraqeb, after a barrel bomb attack there that residents claimed used chlorine gas.

Ayrault laid the blame for the five-year war that has cost nearly 300,000 lives on "the cynical attitude of the (Assad) regime and its supporters who are preventing any political solution in Syria."

Government and opposition forces in Syria have denied using chlorine and have accused each other of doing so.

The government argues that claims that it used chemical weapons are only meant to " serve political agendas".