Afghanistan's new Taliban rulers struggled to keep the country functioning on Wednesday after the final withdrawal of US forces, with foreign donors alarmed about an impending humanitarian crisis.

Two weeks since the Taliban's sweep into Kabul brought a chaotic end to 20 years of warfare, the Islamist militants have yet to name a new government or reveal how they intend to rule.

In an administrative vacuum, prices have soared and crowds have gathered at banks to withdraw cash.