Taliban insurgents have seized Afghanistan's second- and third-biggest cities, local officials said on Friday, as resistance from government forces crumbled and fears grew that an assault on the capital Kabul could be just days away.

A government official confirmed that Kandahar, the economic hub of the south, was under Taliban control as U.S.-led international forces complete their withdrawal after 20 years of war.

Herat in the west also fell to the hard-line Islamist group.