"President Erdogan said that this kind of inhuman attack was unacceptable and warned it risked wasting all the efforts within the framework of the Astana process" to bring peace to Syria, presidential sources said.
The sources did not indicate who was to blame for the attack, describing it as a "chemical weapons attack directed at civilians".
Turkey has been a major foe of President Bashar al-Assad's regime in Syria throughout the Syrian civil war, repeatedly accusing Damascus of war crimes.
The presidential sources said both Putin and Erdogan vowed to keep up joint efforts to preserve the ceasefire.
Erdogan had called Putin to pass on his condolences for the suicide bombing on the Saint Petersburg metro that killed 14 people and both leaders vowed to keep up the fight against terror, the sources said.
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