Syrian President Bashar al-Assad on Thursday said Raqa is not a priority target for his forces, saying his goal is to retake "every inch" of Syrian territory.

"Raqa is a symbol," Assad said in an interview with French media, while asserting that jihadist attacks carried out in France were "not necessarily prepared" in the Islamic State group stronghold in Syria.

"You have ISIS close to Damascus, you have them everywhere," Assad said, using another acronym for the IS.

"Everywhere is a priority depending on the development of the battle," he said, as a new round of peace talks was set to kick off in the Kazakh capital Astana.

"They are in Palmyra now and in the eastern part of Syria," he said in the interview in Damascus with Europe 1 radio and the TF1 and LCI television channels.

"For us it is all the same, Raqa, Palmyra, Idlib, it's all the same."

The Syrian leader said it was the "duty of any government" to regain control of "every inch" of its territory.

After a string of major losses in both Iraq and Syria, the extremists' two main strongholds of Mosul and Raqa are both under attack.

After a massive, four-month campaign, Iraqi forces are tightening the noose on Mosul, while in Syria, an Arab-Kurd alliance, the Syrian Democratic Forces, has begun advancing on Raqa.

While Turkey, Russia and Iran take the lead in the talks in Astana, the West has become "passive", he said, denouncing the coalition for supporting "those groups that represented the terrorists against the government".

"They did not want to achieve peace in Syria."

A new round of the Astana talks was set to kick off on Thursday after a one-day delay for "technical reasons".

The talks are viewed as a warm-up for UN-led negotiations that are due to begin in Geneva on Feb 23.