"Russian military planes were seen all night until morning in several regions of Idlib" in northwestern Syria, said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
"The regime air force bombed eastern sectors of Aleppo," Syria's divided second city, Abdel Rahman told AFP.
The Britain-based monitor says it determines what planes carried out raids according to their type, location, flight patterns and the munitions involved.
Forces supporting Syrian President Bashar al-Assad launched a wide-ranging assault on Tuesday, backed by Russian air strikes, on what they say are jihadist groups.
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Syrian government aircraft struck rebel-held areas of east Aleppo with air strikes and barrel bomb attacks, according to the Observatory and an AFP correspondent.
It was the first government bombardment of Aleppo since October 18.
Russian Defence Minister Sergei Shoigu spoke of a "major operation" which saw the first missions carried out by warplanes taking off from the Admiral Kuznetsov aircraft carrier that arrived off Syria last week.
The offensive drew strong condemnation from the United States, which said it had received reports of hospitals and clinics being bombed.
Once Syria's economic powerhouse, Aleppo has been ravaged by the war that has killed more than 300,000 people across the country since it started in March 2011 with anti-government protests.