Russian President Vladimir Putin has arrived in Tehran for talks with the Iranian leadership expected to focus on the Syrian crisis.
Moscow and Tehran have been the key backers of Syrian President Bashar al-Assad during the country's civil war.
Russia has shielded Syria from international sanctions and on September 30 launched an air campaign against the Islamic State extremist group and other militants, while Tehran has sent military advisers to shore up Assad.
Putin is in the Iranian capital on November 23 for a summit of gas-exporting countries, and is set to meet with Iranian Supreme Leader Ayatollah Ali Khamenei and President Hassan Rohani.
The talks are expected to focus on an international peace plan for Syria that sets a January 1 deadline for the start of talks between Assad and his foes.
The November 23 visit is Putin’s second official trip to Iran. He was last in Tehran in 2007 to attend a summit of Caspian Sea littoral states.
Iran is hosting the 12-country natural gas conference in the wake of its nuclear accord with six world powers, which calls for international sanctions on Iran to be lifted in exchange for curbs on its nuclear program.
Hamid Reza Araqi, the managing director of the National Iranian Gas Company, has said that within four years of the lifting of sanctions Iran hopes its gas exports will equal half the amount that Russia supplied to the European Union in 2014.