Russian warplanes took off from an airbase in western Iran's Hamadan province on Tuesday and conducted an airstrike targeting militants in Syria's Aleppo, Deir al-Zour and Idlib regions, Russia's Defense Ministry said.
It was the first time Russian warplanes used an Iranian airbase for military actions in Syria, TASS reported.
A monitoring group reported the deaths of 31 civilians and 12 rebel fighters in airstrikes on Aleppo, Idlib and Deir al-Zour, although it was not clear whether they were the same strikes or whether they were all carried out by Russian forces.
"Long-range Tu-22M3 bombers and front-line Su-34 bombers that had taken off with a full load of bombs from an airbase in Hamadan conducted a coordinated attack on targets of the terrorist groups Islamic State (Daesh) and al-Nusra Front," the Russian Defence Ministry said in a statement.
Both groups have been designated as "terrorists" by the United Nations. Last month, al-Nusra Front changed its name to Jabhat Fatah al-Sham.
Russia and Iran are longtime allies of the Syrian government, which has been waging war against a range of rebel and militant groups in the country for more than five years.
The attack hit five large storage facilities housing weapons, munitions and fuel, as well as militant training camps around the cities of Saraqib, Al-Bab, Aleppo and Deir al-Zour and three militant command points around the cities of Jafra and Deir al-Zour, the Defence Ministry said.
The pro-opposition Syrian Observatory for Human Rights reported that 12 rebel fighters were killed in Russian airstrikes on a corridor the rebels recently opened into the opposition-held eastern sector of Aleppo.
Another 19 civilians were killed in airstrikes on eastern Aleppo's Tariq al-Bab and Sakhour districts, and 12 more were killed in airstrikes on Deir al-Zour and a town in Idlib province, the Britain-based observatory said.
It could not confirm whether those airstrikes were carried out by Russian or by Syrian government forces, which also carry out regular airstrikes and have less accurate targeting abilities than Russia.
Russian President Vladimir Putin and his Iranian counterpart Hassan Rowhani met last week in Azerbaijan's capital Baku, to strengthen military ties among other discussion points, according to a Kremlin transcript.
Earlier this week, Russian Defence Minister Sergei Shoigu said his country and the United States were "currently in a very active stage of negotiations" to begin joint military action in Syria against Daesh.
Russia and the US have supported opposing sides in Syria, with the US and some Western and regional powers backing certain rebel groups. However, Russia and the US agree on the need to eliminate UN-designated terrorists groups, such as Daesh.
