France is ready to take part in military air operations in Iraq and Syria if necessary, Foreign Minister Laurent Fabius said on Wednesday, Alarabiya reported.
But he said the "modalities" of action in Syria are not the same as in Iraq.
"In Iraq... we support the formation of an inclusive government. We will participate if necessary in an aerial military action," Fabius said in a speech in Paris.
"In Syria, the situation is different: (President) Bashar al-Assad cannot be a partner, because he has an established link" with ISIS.
"That is why we will continue to help the moderate Syrian opposition, which is fighting both" the Islamic State and the Assad regime.
Last week, French President Francois Hollande had raised the possibility of a "political, humanitarian and if necessary military response in accordance with international law" to fight against Islamic State.
Fabius urged an international alliance to fight the dangers posed by ISIS "which could reach our own soil," he said, adding: "Several hundred French jihadists are present in Iraq and Syria."
Last year, France was in the vanguard of states ready to strike the Syrian regime but backed down after the United States decided against military action.
Washington is now in the process of pulling together an international alliance against the militants, present in both Iraq and Syria.
According to French diplomatic sources, what is preventing France from a military intervention in Syria is the lack of an international legal basis.
In the case of Iraq, any military action would have to come at the request of Baghdad and would be backed up by the "self-defence" article in the United Nations charter, according to diplomatic sources.