BEIRUT, Lebanon — Russia resumed airstrikes on the besieged rebel-held sections of Aleppo, Syria, on Tuesday, as it began a major new offensive against insurgents battling Syria's president, Bashar al-Assad. Russia's defense minister, Sergei K. Shoigu, said it had started “a big operation to deliver massive strikes” against the Islamic State and the Levant Victory Front, formerly known as the Nusra Front, in Idlib and Homs Provinces. Jets taking off from Russia's aircraft carrier, the Admiral Kuznetsov, conducted their first strikes on Syria, the Russian military said, noting that its forces were hitting targets in the two provinces. It was unclear whether the strikes on Aleppo were by Russian or by Syrian government warplanes.