Pentagon says group handed ammunition and equipment to al-Qaeda affiliate, purportedly in exchange for safe passage.
France has carried out its first air strikes in Syria against the Islamic State of Iraq and the Levant (ISIL) group.
The announcement from President Francois Hollande’s office on Sunday came after a year of hesitation.
Hollande had resisted the raids in Syria, saying he did not want to strengthen Syria’s President Bashar al-Assad, who is the target of ISIL fighters.
Hollande announced a change in strategy earlier this month because of growing concern about the Syrian refugee crisis that is putting pressure on Europe – the preferred destination for the asylum seekers.
In Iraq, France has been carrying out the air raids since last year as part of the US-led coalition.
Hollande, heading to the UN General Assembly on Sunday where Syrian crisis was expected to be the key subject of debate, stressed the importance of seeking a political solution for Syria.
“More than ever the urgency is putting in place a political transition”, including elements of the opposition and Assad’s regime, Hollande said.
In the lead-up to the UN gathering, John Kerry, US secretary of state, met his Iranian counterpart, Mohammad Javad Zarif, on Saturday to discuss Syria.
Iran and Russia have given strong backing to Assad, whom the US and European countries such as France see as the instigator of a civil war that has left 250,000 dead and large parts of his country in the hands of ISIL.
Speaking to Al Jazeera on Saturday, the EU’s foreign policy chief said Russia intends to step up its military involvement in Syria to prevent the “imminent” collapse of the Syrian government.
Federica Mogherini’s comments followed reports that 500 Russian troops had been deployed to a forward operating base in the Syrian port city of Latakia.
In an interview with Al Jazeera’s James Bays for Talk to Al Jazeera, Mogherini, the EU’s high representative for foreign affairs and security policy, said Sergey Lavrov, the Russian foreign minister, told her his country wanted to prevent the collapse of the Syrian state.
“His fear is of a compete collapse of the state structures in Syria, this could be one of the reasons Russia is talking in this way but it could also be willingness to show that Russia is an important, substantial player,” Mogherini said.