Tuesday's meeting between Russian President Vladimir Putin, Turkish Recep Tayyip Erdogan and Iran's Ebrahim Raisi in Tehran will take place in accordance with the so-called Astana process - talks between the leaders of the three countries aimed at ending the eleven-year war in Syria.
But bilateral meetings are also planned.
Russia hopes to reach a co-operation agreement with Iran, which according to US intelligence is already said to have prepared to sell drones to Russia.
Meets the ayatollah
Just a month ago, Russia's Foreign Minister Sergei Lavrov was in Iran.
He handed over a draft agreement to his Iranian counterpart Hossein Amirabdollahian.
"We hope that, after making some adjustments to the views of the Iranian side, we can be ready to sign it soon," said Kremlin spokesman Dmitry Peskov, according to Russian news agency Interfax in an interview with Iranian state television and radio company. .
Iran and Russia can meet in how both countries have been subject to sanctions from the West.
A collaboration would help reduce the effects of the sanctions, according to Peskov.
Putin is also expected to meet with Iran's supreme leader Ayatollah Ali Khamenei during the trip, which is the second that the Russian president has done since the major invasion of Ukraine in February.
- We hope for a very important dialogue.
Of course, we will be able to discuss bilateral relations, says Peskov.
Looking for green light
The meeting comes at a time when Turkish President Recep Tayyip Erdogan has threatened to launch a new offensive against Kurdish militias in northern Syria.
Russia and Iran support Syrian President Bashar al-Assad in the war, while Turkey backs some rebel groups fighting the government.
Russia has already asked Turkey to refrain from the offensive.
The plans have also been criticized by Iran, whose foreign minister has said they risk becoming a "destabilizing factor in the region", although Iran has also expressed understanding for Turkey's need for a "special operation".
Sinan Ulgen, an expert on Turkish foreign policy at the think tank Carnegie Europe, tells AFP that Erdogan wants to get the green light from Russia and Iran before Turkey re-enters northern Syria - not least because Russia controls the airspace there.
One issue that is not said to be on the agenda in Tehran is the war in Ukraine.
- No, it is not discussed, said Dmitry Peskov during a press conference last week, according to Interfax.