Afghan security forces patrol in the city of Kunduz. (Documentary photo: AFP/VNA)

The insurgents have captured dozens of districts and border crossings in recent months and put pressure on several provincial capitals, including Herat in the west and Kandahar in the south, as foreign troops withdraw.

The offensive has gathered momentum in recent days after the United States announced it would end its military mission in the country by the end of August.

Taliban fighters seized key government buildings in Kunduz, leaving government forces hanging onto control of the airport and their base, a provincial assembly lawmaker said on Sunday, raising fears it could be the latest to fall to the Taliban.

The city is regarded as a strategic prize as it lies at the gateway to mineral-rich northern provinces and Central Asia.