As per the assessment by US intelligence agencies, the Taliban is closing in on Kabul and could isolate the city in 30 days, and take control of the Afghan capital in 90 days.
"But this is not a foregone conclusion," a defence official said. He also added that the Afghan security forces could reverse the momentum by putting up more resistance against the insurgent group.
The warning comes amid reports of Taliban forces taking control of eight provincial capitals. The last two cities to fall were Farah, capital of the same-named province, and Pul-e-Khumri in Baghlan.
Six of the other provincial capitals to have fallen since Friday are in the country's north, with the insurgents setting their sights on Mazar-i-Sharif, the region's biggest city.