The Russian ministry of defence said planes had struck targets in Aleppo, Deir ez-Zor and Idlib provinces on Tuesday.
A spokesperson said long-range Tu-23M3 long-range bombers and Su-34 fighters took off from a base in Hamadan to strike “targets belonging to the Islamic State and Jabhat al-Nusra terrorist groups”.
It said command centres, training camps and weapons depots were destroyed in Saraqib, al-Bab, Aleppo and Deir ez-Zor cities, and a “significant number" of militants killed.
Much of Idlib province including Saraqib is controlled by the former Jabhat al-Nusra group, which has renamed itself as Jabhat Fateh al-Sham after announcing a supposed spilt from al-Qaeda.
Its militants are leading a coalition of Islamist groups fighting to break the siege on rebel-held areas of Aleppo city, which is home to local opposition groups.
The rebrand was seen as a ploy to stop its fighters being targeted by international air strikes and gain local support, but Russia continues to refer to them as “terrorists”.
Much of the area around Deir ez-Zor city is controlled by Isis amid a Syrian regime advance, while al-Bab is expected to be the next target of the US-backed Syrian Democratic Forces campaign against the so-called Islamic State.
Russian air strikes are alleged to have caused the deaths of more than 2,000 civilians since the start of Vladimir Putin’s intervention in the conflict in September.
The United Nations has repeatedly called on all parties in the civil war to adhere to international laws and protect civilian lives and infrastructure, following the bombing of numerous hospitals and medical facilities.
Recent days have also seen the alleged use of chlorine gas on a rebel-held area of Aleppo in an attack blamed on Syrian government forces.
Russia and Iran are both supporting President Assad in the conflict, while the US-led coalition is targeting Isis and supporting some rebel groups.
Russia has admitted deploying special forces in Syria but characterised their role as “advisers”, despite several combat deaths, while Iran has also sent members of the Islamic Revolutionary Guard Corps (IRGC) and is alleged to by funding Shia militias fighting in both Syria and Iraq.
Tensions between Washington and the Kremlin have increased after the alleged Russian bombing of US-backed rebels who were fighting Isis.
On Monday, Russian defence minister Sergei Shoigu said commanders were “nearing an agreement” to end the fighting in Aleppo city with American officials.
But Elizabeth Trudeau, from the US State Department, said there was no agreement to announce, adding: “We do speak regularly with Russian officials about way to strengthen the cessation of hostilities, improve humanitarian access and bring about conditions necessary to find a political solution.“
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