The US military has said it could slow down its withdrawal from Afghanistan in light of recent battlefield victories by the Taliban.
Pentagon spokesman John Kirby said the deadline for a full withdrawal by 11 September was still in place, but the pace may change, reports the BBC.
Pentagon officials said last week that the withdrawal is about half-way done.
Afghanistan has seen increasing violence as the US and Nato prepare to pull out their remaining troops.
Over the last month, the Taliban have intensified their attacks and gained control of more than 30 districts. The hardline Islamist group has also seized large quantities of military equipment, according to local media, and killed, wounded or captured dozens of troops.
Afghan government spokespeople have denied that the districts have fallen to the Taliban, saying they were evacuated in a "tactical withdrawal". It is unclear how many Taliban have been killed or wounded.The Taliban say they have control of the whole northern province of Kunduz, with only the provincial capital retained by the government.
Police said the group had encircled the strategically important city, also named Kunduz, the Associated Press reported. A long-standing target, it briefly fell to the insurgents in 2015 before being retaken by Nato-backed government forces.
Afghan security forces continue to resist the Taliban push, and recaptured two districts in the north-eastern province of Takhar on Sunday.