Afghan President Ashraf Ghani says he will not give up the "achievements" of the last 20 years and that "consultations" are under way.
He made the announcement during a brief, televised address, his first public appearance in days following a major Taliban advance.
The insurgents have seized most of northern, western and southern Afghanistan and are battling government forces south of Kabul.
There are reports Mazar-e-Sharif, the fourth-largest city in Afghanistan, also fell to the Taliban on Saturday after a multipronged assault launched by insurgents.
It comes as about 600 British personnel have deployed to the country to support the evacuation of British Nationals from Afghanistan and aid the evacuation of former British staff eligible for relocation under the Afghan Relocation and Assistance Policy (ARAP).
The Taliban have captured much of northern, western and southern Afghanistan in recent weeks, leaving the Western-backed government in control of a smattering of provinces in the centre and east, as well as the capital, Kabul.
The Taliban are currently battling government forces just miles south of Kabul.
The first US military personnel from a contingent of 3,000 arrived on Friday to help partially evacuate the US Embassy.
A Taliban offensive has gathered momentum in recent weeks, as NATO forces have prepared to finalise a withdrawal from Afghanistan.
Cover image: President Ashraf Ghani (Picture: US Department of State).