BEIRUT — The Islamic State group has retaken large areas in the northern Syrian province of Raqqa that it recently lost to government troops, opposition activists said Tuesday.

Syrian troops have been on the offensive for nearly three weeks and had approached to within four miles of the Tabqa air base near Raqqa city, the de facto capital of the self-declared caliphate of the group that is also known as ISIS or ISIL.

But the Britain-based Syrian Observatory for Human Rights said Tuesday that government forces lost all the territory they gained in Raqqa province since launching their offensive on June 2, adding that troops have been pushed back now to about 25 miles from Tabqa.