PARIS (Reuters) - France is working to find a way for the International Criminal Court’s prosecutor to launch an investigation into war crimes it says have been committed by Syrian and Russian forces in eastern Aleppo, Foreign Minister Jean-Marc Ayrault said on Monday.

A boy runs as he rushes away from a site hit by what activists said were airstrikes by forces loyal to Syria's President Bashar al-Assad in the Douma neighborhood of Damascus, Syria August 24, 2015. REUTERS/Bassam Khabieh

Since the collapse of efforts to reach a ceasefire in September, Russian and Syrian warplanes have launched their biggest offensive on Aleppo’s besieged rebel-held sectors, in a battle that could become a turning point in the five-year-old civil war.

“These bombings - and I said it in Moscow - are war crimes,” Ayrault told France Inter radio after a French-drafted United Nations Security Council resolution on Syria was vetoed at the weekend by Russia. “It includes all those who are complicit for what’s happening in Aleppo, including Russian leaders.

“We shall contact the International Criminal Court prosecutor to see how she can launch these investigations.”

U.S. Secretary of State John Kerry also called for a war crimes investigation last week.

It is unclear how the ICC could proceed given that the court has no jurisdiction for crimes in Syria because it is not a member of the ICC.

It appears the only way for the case to make it to the ICC would be through the U.N. Security Council referral, which has been deadlocked over Syria. Moscow vetoed a French resolution in May 2014 to refer the situation in Syria to the ICC.

“It is very dangerous to play with such words because war crimes also weigh on the shoulders of American officials,” said Russian Foreign Ministry spokeswoman Maria Zakharova, according to RIA news agency.

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ICC OPTIONS

A French diplomatic source acknowledged the difficulties, but said Paris had begun to comb through the ICC’s articles to see what could be done.

The source said the ICC would have jurisdiction if an alleged criminal had the citizenship of an ICC member, for example a dual Syrian-French national in the government involved in an attack. It would be the job of the relevant member state to bring a prosecution.

The source said it would also study whether the ICC could have jurisdiction if a victim of an attack had citizenship of an ICC member.

“It will be complicated, but we are looking for other solutions. Our jurists are trying to find other ways,” the source said, adding that Paris was also not ruling out a new Security Council resolution on accountability.

Ayrault said Paris would also seek separate sanctions on the Syrian government at the United Nations once a joint U.N. and Organization for the Prohibition of Chemical Weapons (OPCW) inquiry concludes on Oct. 21.

The inquiry has identified two Syrian Air Force helicopter squadrons and two other military units it holds responsible for chlorine gas attacks on civilians, Western diplomats have told Reuters.

The diplomatic source said a U.S.-drafted Security Council resolution on the use of chemical weapons would now be discussed, although it was vital to reach a deal with Russia.

“It would be problematic to have a veto on chemical weapons. It would be serious, but until now the Russians have been on board with regard chemical weapons,” the source said.

French officials have grappled for ways to try to put new pressure on Russia and their growing anger at events in Aleppo have led them to reconsider whether to host him on Oct. 19.

“We do not agree with what Russia is doing, bombarding Aleppo. France is committed as never before to saving the population of Aleppo,” Ayrault said.

“If the President decides (to see Putin), this will not be to trade pleasantries,” he added.