Russian President Vladimir Putin will visit Tehran on Tuesday to discuss with his Iranian and Turkish counterparts the war in Syria.
Russia, Turkey and Iran have in recent years met to discuss Syria as part of the so-called "Astana peace process".
All three nations are involved in the conflict, which has lasted for more than a decade in the Arab country.
While Russia and Iran support the Damascus regime, Turkey backs the rebels.
Tuesday's summit comes as Turkish President Recep Tayyip Erdogan threatens to start a new offensive in northern Syria against Kurdish militants.
Iran, whose President Ebrahim Raisi is hosting the meeting, has already warned that any Turkish military action in Syria could "destabilise the region".
The Tehran summit will also enable Mr Erdogan to have his first meeting with Mr Putin since Russia invaded Ukraine in February.
The Turkish president has for months offered to meet the Russian leader to try to help resolve heightened global tensions since the war began.
"The timing of this summit is not a coincidence," Russian analyst Vladimir Sotnikov told AFP.
"Turkey wants to conduct a 'special operation' in Syria just as Russia is implementing a 'special operation' in Ukraine," he said.
Turkey has launched waves of attacks on Syria since 2016, targeting Kurdish militias as well as ISIS and forces loyal to Syrian President Bashar Al Assad.
Mr Erdogan's planned military offensive targets Kurdish fighters that Ankara regards as terrorists, including the Kurdish People's Protection Units (YPG), which form a crucial part of the US-backed Syrian Democratic Forces that helped to defeat ISIS in northern Syria.
Ankara fears a strong Kurdish presence along its border with Syria will embolden the banned Kurdistan Workers' Party, which for decades has been waging an insurgency against the Turkish state that has claimed tens of thousands of lives.
Syria's government has repeatedly condemned Turkish threats to mount a new incursion.
Sinan Ulgen, a visiting scholar at Carnegie Europe who specialises in Turkish foreign policy, said Ankara wants the blessing of Moscow and Iran before launching its operation.
"It's particularly important because the two potential target regions are under the control of Russia, and Turkey wants to be able to use the airspace ... so as to minimise the risks," he said.
Iran "also has an indirect presence in the region through Shiite militias that it controls", said Mr Ulgen.
Ultimately, Mr Erdogan is hoping to get "the green light" from Mr Putin and Mr Raisi, he added.
Russia has already expressed the hope that Turkey will "refrain" from launching an attack on Syria.
Iran, whose foreign minister Hossein Amirabdollahian visited both Ankara and Damascus in recent weeks, has also urged caution.
Late last month, Iran's top diplomat said in Ankara that "we understand that ... maybe a special operation might be needed".
"Turkey's security concerns must be tackled fully and permanently."
Days later, Mr Amirabdollahian said in Damascus that Turkish military action in Syria "would be a destabilising element in the region".
Mazloum Abdi, chief commander of the YPG-linked Syrian Democratic Forces, has urged Russia and Iran to restrain Turkey.
"We hope [the attacks] will not take place and that the Kurds ... will not be forsaken during the talks between the big powers," he said.
The SDF has warned that an invasion by Ankara would undermine efforts to combat ISIS in north-east Syria.
Nicholas Heras of the Newlines Institute said Iran and Russia "want to prevent another Turkish military campaign in Syria".
"Iran is building a presence in and around Aleppo that concerns Turkey, and Russia is for all intents and purposes ceding ground to Iran throughout Syria," he added.
For Iranian political analyst Ahmad Zeidabadi, "new differences" have emerged between Russia, Iran and Turkey following the Ukraine war.
This and an "uncertain future", he said, means the three leaders will try to "co-ordinate" their views on Syria to avoid further tensions.
