French President Francois Hollande has warned the West against working with Syria's president in the fight against the Islamic State (IS) group, saying Bashar al-Assad was a principal ally of the fighters who have taken over large areas of Syria and Iraq.
In a speech on Thursday, Hollande rejected any co-operation with Assad, saying the situation in Syria required a "military and humanitarian" response.
"Assad cannot be a partner in the fight against terrorism, he is the de facto ally of jihadists," he said.
Assad cannot be a partner in the fight against terrorism, he is the de facto ally of jihadists.
"There is no choice to be made between two barbarisms."
Hollande's comments come days after Assad's regime said it was willing to work with the international community, including the US, to tackle fighters in the war-ravaged country.
France has recently admitted providing weapons to the 'moderate' Syrian opposition, but there are reported differences between Paris and Washington on whether there should be more support in the future as efforts to fight the Islamic State in Syria increase.
The US has already carried out reconnaissance flights on IS positions in Syria in surveillance seen as a precursor to possible air strikes against the group, which it is already carrying out in neighbouring Iraq.
Hollande's comments come as a group monitoring the violence in Syria said IS fighters had executed dozens of Syrian army soldiers taken hostage after capturing an air base in the northeast of the country.
IS stormed the Tabqa air base on Sunday after days of clashes with the army in one of the fiercest confrontations yet between the two sides.
Videos posted online on Thursday purportedly showed IS fighters making scores of Syrian army hostages walk and run through the desert in their underwear.
The video showed at least 135 men, some with their hands on their heads, running barefoot through a desert landscape as armed men jeered them.
The Syrian Observatory for Human Rights said the soldiers were executed after trying to escape from the airport when they were taken hostage.
Tabqa was the army's last foothold in an area otherwise controlled by the IS group.
Meanwhile the mother of kidnapped US journalist, Steven Sotloff, has pleaded for the life of her son held hostage by IS, just over a week after the group beheaded a fellow US reporter and threatened more murders.
In a video released on Wednesday, Shirley Sotloff directly addressed the group's leader, Abu Bakr al-Baghdadi, saying her son was "an innocent journalist" who had no control over US policy in the Middle East.
Syrian rebel forces have been fighting Assad for more than three years in a war the UN estimates to have has cost at least 190,000 lives.