Iranian television reported that the three leaders would each have "bilateral meetings" on the sidelines of the main summit.
"The Tehran summit can produce peace and reconciliation in Syria or it can deepen the mess created by endless bouts of violence mainly instigated by the Assad regime", Ilnur Cevik, a senior adviser to Erdogan, wrote in the Daily Sabah newspaper.
While Turkish leader Erdogan proposed a ceasefire in the rebel-dominated bastion of Idlib in northwestern parts of Syria, President Putin affirmed that Russian Federation opposes the call for any truce with the rebels in the hope that the rebels opposing Assad's rule "would have the common sense to lay down their weapons and surrender".
"In the past 18 months I have stood on this floor twice, promising that the United States would respond to the use of chemical weapons in Syria", she said.
A major assault would be devastating for the almost three million people living in the northwestern province, many of them rebels and civilians who were moved out of other areas as they came back under regime control.
"The United States is closely monitoring the situation in Idlib province, Syria, where millions of innocent civilians are under threat of an imminent Assad regime attack, backed by Russian Federation and Iran", the White House said in a statement on Tuesday.
"The least the summit can do is to prevent this military war", he said.More news: I'm suprised Ronaldo left Real Madrid - Messi
For Turkey, the stakes couldn't be higher.
Activists and residents say warplanes struck areas on the southern edge of Idlib province on Friday, killing one and causing loud explosions and large plumes of smoke.
Jeffrey said an attack by Russian and Syrian forces, and the use of chemical weapons, would force huge refugee flows into southeastern Turkey or areas in Syria under Turkish control.
Turkey also does not want to see another Kurdish-controlled area rise along its border, as it already faces in northern Iraq.
"You still need moderate opposition groups who represent the Sunni suffering masses in Syria to achieve a viable political solution and durable peace in this country", he wrote. Russia, which has provided air support to the Syrian Army since 2015, has made a big show of force by moving 10 warships and two submarines off the coast of Syria. While Idlib is expected to top the agenda, the trio are also expected to discuss mechanisms for minimizing the impact of United States financial pressure.
The UN has warned that an all-out offensive in Idlib will lead to death and destruction even greater than that seen previously in Syria, including the displacement of another 800,000 civilians - most of whom are likely to seek refuge in nearby Turkey, which already hosts 3.5 million war refugees.
The Trump administration's new envoy to Syria, Jim Jeffrey, told the Reuters news agency this week that he was "very sure that we have very, very good grounds to be making these warnings" about an upcoming assault on Idlib, and that while "any offensive is to us objectionable as a reckless escalation".
The Syrian military has been urging the rebels in Idlib to surrender.
"Assad's brutal regime - backed by Russian Federation and Iran - can not continue to attack and terrorize Syria's citizens".