Turkish Foreign Minister Mevlüt Çavuşoğlu discussed the Syrian constitutional committee with his Iranian counterpart Mohammad Javad Zarif, according to the diplomatic sources on Sunday.
Speaking over the phone, the two top diplomats also discussed the Astana meeting, sources added.
The Astana peace process, aimed at ending the Syrian conflict, was launched in January 2017 by Russia and Iran, allies of the regime, and Turkey.
Syria has been locked in a vicious civil war since early 2011, when the Bashar al-Assad regime cracked down on pro-democracy protests with unexpected ferocity.
Since then, hundreds of thousands of people have been killed and more than 10 million others displaced, according to UN officials.