The capture of Pul-e-Khumri would cut the main north-south road through the centre of Afghanistan, leaving the remaining Taleban forces in the north stranded.
The opposition forces further claim to have seized the strategic town of Pul-e-Khumri, north of Kabul, and the town of Qala-e-Nau in the western province of Badghis.
The Alliance said Taleban commanders south of Pul-e-Khumri had defected, weakening the garrison in the town of Bamiyan - the Taleban's main base in the central highlands.