PARIS — French President Francois Hollande warned Syrian President Bashar al-Assad on Monday that any use of the country's chemical weapons would be a legitimate justification for military intervention.

"With our partners we remain very vigilant regarding preventing the use of chemical weapons, which for the international community would be a legitimate reason for direct intervention," Hollande said during an annual foreign policy speech to French ambassadors.

The comments followed President Barack Obama's warning to Syria on Aug. 20 that military intervention could be justified if Assad's government used unconventional weapons or moved them in a threatening fashion.

"What's at stake goes beyond Syria. It concerns the security of the Middle East and especially Lebanon," Hollande said.

France, an outspoken critic of Assad's government, will this week chair a meeting of foreign ministers at the U.N. Security Council focusing primarily on humanitarian issues.

Hollande said Paris was still working on efforts to return to the Security Council for a new resolution. He criticized Russia and China, who have vetoed three resolutions, over their continued support for Assad.

"I say to China and Russia: [Your] attitude is weakening the capacity to ensure the United Nations charter is respected," he said.

Hollande, who has increasingly come under fire at home for a perceived passive approach to the crisis, urged the opposition to create a representative provisional government which his country would immediately recognize once it was formed.

He said Paris supported people on the ground who wanted a free, democratic Syria and were protecting civilians.

"We are also helping those who are organising the liberated zones on Syrian territory and it is the buffer zone initiative proposed by Turkey that we are working on," Hollande said.

French Foreign Minister Laurent Fabius, who will chair this week's U.N. meeting, suggested on Monday a no-fly zone may become an inevitability if refugee numbers continued to soar.

Turkey, already hosting at least 80,000 Syrian refugees, fears an overwhelming influx and says that may force it to create such a zone.

However, it is reluctant to act unilaterally on what would amount to military intervention, and the idea of a buffer zone has so far gained little traction elsewhere.