He told Al Jazeera that Erdogan's warning that Turkey would act unilaterally against the SDF if the US did not accept its demands in Syria's northeast within two weeks indicated it had Russian backing.
"It leaves Turkey, Assad, Russia and Iran to have a four-power resolution in Syria," Sazak said. "Turkey, by giving the US a two-week deadline is turning up the heat and if the Americans drag their feet, they'll go with Russia."
'A win for Moscow and Assad' Al Jazeera
Ahmet Evin, professor emeritus at Istanbul's Sabanci University, was quoted by Al Jazeera as saying the committee would benefit al-Assad.
"It's clearly a two-to-one majority and writing a constitution essentially does two things - it internationally democratises the regime and also legitimises it," he said. "I think Moscow is right on target and it's a win for Moscow and [al-]Assad."
"There won't be any reaction to this in the US because it used to have a bad Middle East policy and now it has no Middle East policy," Evin said.
The leaders also suggested the Astana talks could now be used as a template for other conflicts in the region, such as Yemen. "This gives the opportunity for Russia to make itself an important power and conflict resolution agent in a region in which the US has failed," Evin added.
Kamal Alam, a London-based military analyst specializing in Syria and Turkey, told Al Jazeera the creation of a constitutional committee "doesn't change anything on the ground". "Out of the three countries, Russia is the loud and clear winner here. Iran is a pariah at the moment while Turkey is stuck in the middle of Europe, America and Russia," Alam said. "Russia is in the driving seat and that means al-Assad and the Syrian government are in a better position."
Syrian Negotiation Commission Al Jazeera
Yahya al-Aridi, spokesman for the Syrian Negotiation Commission - the main political opposition bloc was quoted by Al Jazeera as saying, all parties involved in the long-running conflict view the constitutional committee as the "gate" through which a political solution can be achieved.
While the committee for the al-Assad government and ally Russia is considered "the crowning of their military efforts", al-Aridi noted that for the opposition, it is the first step towards implementing United Nations Security Council resolutions that safeguard the rights of Syrians.
"It is the only game in town," he said of the committee. "It will not grant the opposition or Syrians full rights " but at least it puts Syria back on track on issues related to freedom and democracy," Aridi added.
The leaders also condemned the U.S. decision to recognize Syria's occupied Golan Heights as Israeli territory, which in addition to violating international law, also threatens regional peace and security, according to a joint statement.
US President Donald Trump on Monday March 25, 2019 formally recognized Israeli sovereignty over the Israel-occupied Golan Heights, reversing decades of United State's policy.
The announcement came as Benjamin Netanyahu visited the White House in a trip the Israeli prime minister said he cut short after an early morning rocket, allegedly fired from the besieged Gaza Strip, struck a home in central Israel, wounding seven people.