The Taliban seized the cities of Ghazni and Herat on Thursday, in the most dramatic string of captures since launching their offensive.
Taking the strategically important Ghazni increases the likelihood the Taliban could take the capital Kabul.
There is also heavy fighting in the second-largest city, Kandahar.
The insurgents have moved at speed, seizing new territories almost daily, as the US and other foreign troops withdraw after 20 years of military operations.
The city of Qala-I-Naw also fell to the Taliban, who now control about a third of the country’s regional cities and most of northern Afghanistan. The group’s rapid advance has dealt a crushing blow to government security forces.
Sources have told the BBC that Lashkar Gah, the capital of Helmand province, is also now in the hands of the Taliban, though this has not been confirmed.
Thousands of civilians have been displaced, fleeing to Kabul to try and escape the fighting.
Taking Ghazni is a significant gain due to its location – it is 150km (93 miles) from Kabul, and is on the major Kabul-Kandahar motorway, linking militant strongholds in the south to Kabul.
A provincial council member in the city told the BBC that the Taliban had taken most of the center, with only a police base on the outskirts controlled by the Afghan security forces.
Herat, which has been under siege for weeks, is also a major win for the militants. It is Afghanistan’s third-largest city, lies on significant ancient trade routes, and is seen as the gateway to Iran.
On Thursday, a video on social media showed the insurgents running through a central Herat street firing their weapons, and the Taliban flag was seen flying over the police headquarters. A regional council member confirmed to the BBC that the city had fallen to the militants.
Herat, which has been under siege for weeks, is also a major win for the militants. It is Afghanistan’s third-largest city, lies on significant ancient trade routes, and is seen as the gateway to Iran.
On Thursday, a video on social media showed the insurgents running through a central Herat street firing their weapons, and the Taliban flag was seen flying over the police headquarters. A regional council member confirmed to the BBC that the city had fallen to the militants.