Russian Foreign Minister Sergei Lavrov was due in Iran Wednesday for talks on boosting trade and energy cooperation as the two countries grapple with Western economic sanctions.
Tehran and Moscow both have huge oil and gas reserves but are constrained by sanctions that limit their ability to export their output.
"Lavrov will meet our foreign minister (Hossein Amir-Abdollahian) tomorrow (Thursday)," Iran's official IRNA news agency said.
Russia was slapped with sanctions following its February invasion of neighbouring Ukraine, while Iran's economy has been reeling under biting sanctions reimposed by the US in 2018, following Washington's withdrawal from a nuclear accord between Tehran and major powers.
Russia played a key role in that deal, taking charge of Iran's excess enriched uranium stocks beyond those permitted under the agreement.
It has been party to stumbling talks between Iran and the powers on reviving the 2015 deal with renewed US participation.
The negotiations have been stalled since March amid sharp differences between Tehran and Washington on the US sanctions that would be lifted in exchange for Iran's return to full compliance with the agreed limits to its nuclear activities.
Iran's President Ebrahim Raisi visited Moscow in January, and said he had presented his counterpart Vladimir Putin with draft documents on strategic cooperation that would cement collaboration for the next two decades.
In late May, Russian Deputy Prime Minister Alexander Novak visited Tehran at the head of a large delegation after Russia's invasion of Ukraine sent global oil and gas prices soaring.