PARIS (AFP) - France's defence minister said extremists from ISIS (Islamic State in Iraq and Syria) were making major gains in Syria, especially in the northern region of Aleppo.

In parliament, Jean-Yves Le Drian pointed to "the very significant progress of Daesh (ISIS) in Syria at this very moment," as he defended France's decision to conduct surveillance flights over Syria with a view to carrying out air strikes. "I'm thinking in particular of what is currently happening in the Aleppo region.

"There is an extremely strong offensive taking place on the small town of Marea, which if it succeeded would wipe out what we still call the Free Syrian Army or the national Syrian coalition, or what is left of it."

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

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.

Le Drian once again ruled out any ground intervention in Syria, but said Paris would support any such operation by countries in the region.

"The only possibility is that Syria's opposition forces mobilise with the support of countries in the region.

"Then there could be support from France and the coalition's countries."

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

The United States, Canada, Turkey and Gulf states have already been involved in strikes on ISIS militants in Syria.

Australia also announced last week it would join the Syrian operation.