Russia on Tuesday launched bombing attacks on the Islamic State groups in Syria from an Iranian air base, as fighting raged for control of the ravaged city of Aleppo, further complicating its engagement in the Middle East conflict.
Russia also became the first foreign military power to operate from Iran's soil since World War II after a fleet of TU-22 long-range bombers bound for Syria flew out from the Iranian air base.
Russia's defence ministry said long-range warplanes took off from Hamedan base in western Iran and "conducted a group air strike against targets of the Islamic State and Jabhat al-Nusra terrorist groups in the provinces of Aleppo, Deir Ezzor and Idlib".
The strikes destroyed jihadist targets, including weapons depots and command centres, "killing a large number of fighters," Moscow said.
But, separate reports from the Syrian Observatory for Human Rights said 23 civilians were killed in Russian and Syrian strikes on rebel-held areas in Aleppo, Syria's second largest city.
Nine civilians were also killed in government-held areas by rebel shelling, it said.
The use of Iranian base marks a departure from the bombing campaign that Kremlin launched in September to support Syrian leader Bashar al-Assad, as Moscow had been using its bases in Syria and Russia for air raids.
Tehran, which is also backing the Assad regime, has thousands of troops fighting on the ground while Russia provides air power.
Both oppose calls for Assad to step down as a way of resolving the conflict that has killed more than 290,000 people since it erupted in March 2011.
But this could antagonise the United States and its western allies as the Russian move makes the Syrian crisis even more difficult.
The US, however, credited Moscow with having given it a brief advance warning on the likely strike from Iranian bases.