On Sunday, Islamists captured the strategically important provincial capital of Kunduz and two other northern capitals.
Now the Taliban have also taken Aibak, the city's deputy governor announced on Monday.
It is the sixth provincial capital that the movement has conquered since last Friday.
Expressen's war correspondent Magda Gad describes the fear among the population as enormous.
- I really want to emphasize that the situation in the country is terrible, she says to SVT: Morgonstudion.
"There is no military solution"
Despite the Islamists taking control of ever larger parts of Afghanistan, NATO and international forces continue to withdraw from the country.
This is stated by an official from the defense alliance for the news agency Reuters on Monday.
"There is no military solution to the conflict and the Taliban must understand that they will never be recognized by the international community and they reject the political process and try to take the country by force," he said.
According to NATO, the solution is for the Taliban to stop their attacks and participate in peace talks.
Pakistan strikes back
Kabul and several Western governments have blamed Pakistan for the Taliban's failure to survive 20 years of war.
But instead of pointing the finger at them for the rapidly deteriorating situation, Pakistani Foreign Minister Shah Mehmood Qureshi calls on the international community to investigate the "collapse" of the Afghan security forces.
- The lack of will to fight, the capitulation we see in Afghanistan, can we be held responsible for it?
No, we can not, Qureshi said at a press conference, adding that according to Reuters, Pakistan supported a political solution to bring peace to Afghanistan.
Other countries in the region, including Afghanistan, have also blamed the Taliban's success on what they called a hasty and unconditional withdrawal of foreign troops.