The Taliban have claimed the capture of Afghanistan's second largest city, Kandahar, in what would be a major win for the militants.
Several cities fell on Thursday in the most dramatic string of victories yet.
The United States said it is sending nearly 3,000 troops back into Afghanistan to help evacuate staff from the American embassy.
The US said it was sending troops to the airport in Kabul to help evacuate a "significant" number of embassy staff on special flights.
The UK said it was also deploying about 600 troops on a short-term basis to provide support to British nationals leaving the country. The number of staff working at the British embassy in Kabul has a been reduced to a core team, BBC reported.
The insurgents have moved quickly, seizing new territories as US and other foreign troops withdraw after 20 years of military operations.
The Taliban now control most of northern Afghanistan and about a third of the country's regional capitals.