French President Francois Hollande, whose country is carrying out surveillance flights over Syria, said Monday it would be "necessary" to carry out air strikes against ISIL militants.

French President Francois Hollande, whose country is carrying out surveillance flights over Syria, said Monday it would be "necessary" to carry out air strikes against militants of the Takfiri group, ISIL (so-called Islamic State in Iraq and Levant),there.

"We announced surveillance flights that would allow us to prepare air strikes if they were necessary, and they will be necessary in Syria," he told journalists after talks with Nigerian President Muhammadu Buhari.

France has been part of a US-led coalition bombing ISIL positions in Iraq for the past year, but Hollande changed strategy last week to expand action to Syria as political pressure mounts over the Takfiri threat faced by France.

Hollande said last week he had ordered surveillance flights because he wanted to find out "what is being prepared against us and what is being done against the Syrian population".

Hollande's move to carry out air strikes in Syria also comes as Europe is buckling under the pressure of a flood of refugees from the war-torn country.

France has so far confirmed it has carried out two surveillance flights over Syrian territory.