SYRIAN President Bashar al-Assad is prepared “to negotiate everything” at talks set to begin in Kazakhstan, as he seeks to cast himself as a peacemaker after his forces recaptured Aleppo last month.

However, the upcoming talks, brokered by Turkey and Russia, are still in doubt as Syrian opposition groups have yet to confirm their participation.

In comments to the French press from his Damascus palace, al-Assad also defended his troops over the deadly bombardment of eastern Aleppo, saying the alternative would have been to leave the city’s civilians to the mercy of “terrorists” – a term the government uses for all opposed to al-Assad’s rule.

Assad questioned the credibility of Syrian opposition groups backed by the west and Saudi Arabia, which make up the bulk of the armed and political opposition to his rule.

“There’s no limit to negotiations,” he said. “But who is going to be there from the other side, we don’t know yet ... the viability of the conference depends on that.”

Past Syrian peace talks have run aground on the question of al-Assad’s future and whether he is to continue as president.

The opposition have always insisted his departure is a precondition for any reforms.

Assad said the matter could only be resolved through a constitutional referendum.

“My position is related to the constitution,” he said. “If they want to discuss this point, they need to discuss the constitution.

“You need a referendum for every constitutional amendment. This is one of the points that could be discussed in the meeting in Kazakhstan.”

The talks are scheduled to begin in the Kazakh capital of Astana on January 23. They follow a lengthy rapprochement between Russia, a key backer of Assad, and Turkey, a main sponsor of the opposition.

That culminated in a ceasefire agreement which came into force on December 30, but that has already started to erode.

The US is excluded from the talks, and Russian officials have suggested US officials could be invited at a later date.

On Aleppo, al-Assad said government fighters were forced “to liberate” the city.

“And there is a price, sometimes, but at the end the people are liberated from the terrorists,” he added.

Once Syria’s largest city and industrial hub, Aleppo has been devastated by nearly six years of war.

Rebels took control of its eastern districts in 2012, before surrendering it to government authority last month. The UN said the government’s relentless military campaign, which displaced tens of thousands of civilians, may have violated the laws of war.