Turkey is one of the guarantors of the Syrian ceasefire, brokered also by Russia and Iran.

"Assad is definitely a terrorist who has carried out state terrorism," Turkish President Recep Tayyip Erdogan said at a televised news conference with his Tunisian counterpart Beji Caid Essebsi in Tunis.

"It is impossible to continue with Assad. How can we embrace the future with a Syrian president who has killed close to a million of his citizens?" he said.

The Syrian Foreign Ministry has responded to the accusations by saying that Erdogan is misleading the public opinion in Turkey by claiming that Assad should not remain in power, adding that Ankara's policy "causes catastrophic consequences" for both countries.

"Once again, Turkish President Erdogan continues to mislead the public opinion in Turkey. With his useless soap bubbles, he tries in vain to justify the crimes he has committed against the Syrian people by infinitely and comprehensively helping the terrorist groups in Syria," the ministry's statement read, as quoted by the SANA news agency.

Assad himself has repeatedly denied allegations of targeting civilians.

Despite Turkey being a mediator in the Syrian peace talks, which are also brokered by Russia and Iran, Assad has previously refused to consider Ankara as its partner or a guarantor state, accusing the country of supporting terrorism.

For its part, Ankara has been sending mixed signals concerning its view of Syria's political future. In November, Erdogan stated that Turkey was not ruling out future contacts with Assad, with the statement following the announcement that Ankara no longer considers Damascus a threat. However, since the civil war’s beginning in Syria in 2011, Turkey, along with many regional states, as well as the US, has been calling on Assad to step down.

READ MORE: Erdogan Does Not Rule Out Future Contacts With Assad on Syrian Kurds – Reports

This summer, Turkey set up observation points in Syria's Afrin and deployed troops there in order to support the anti-terrorist operation conducted by the Free Syrian Army, which has been the second joint campaign on the ground by the forces in the course of a year. While Ankara said that the operation was agreed at the Astana talks, Damascus accused Turkey of "aggressive actions" that violate the international law.