Activists say Syrian troops backed by Russian airstrikes are battling insurgents in central Syria.

The Britain-based Syrian Observatory for Human Rights says a government offensive began on four fronts Wednesday in the northwestern provinces of Idlib and neighboring Hama. Observatory director Rami Abdurrahman says it is "the most intense fighting in months."

Activist Ahmad al-Ahmad, who is currently in Idlib, says government troops are "heavily" shelling central areas after rebels attacked an army post and destroyed a tank.

The latest developments come exactly a week after Russia began launching airstrikes in Syria.

Moscow says it is targeting the Islamic State group and al-Qaida's Syrian affiliate, but at least some of the strikes appear to have hit Western-backed rebel factions.