BEIRUT — With waves of air attacks and missile strikes, Russian forces launched a major new offensive Tuesday against rebel-held areas in Syria, as activists reported the first airstrikes in nearly a month on the battered and besieged eastern districts of Aleppo.

A Russian carrier group off Syria — ordered to the Mediterranean Sea by Russian President Vladi­mir Putin in a show of support for Syrian leader Bashar al-Assad — unleashed its considerable firepower, and government forces tightened their siege on rebel-held Aleppo.

Russia’s Defense Ministry denied involvement in the attacks on Aleppo, saying it has been nearly a month since Russian forces launched strikes on the city.

The divided northern city has become the epicenter of the battle for Syria, as one of the last urban bastions of factions opposing Assad. The government’s recapture of Aleppo could hasten the fall of remaining rebel strongholds across the country.