"DEEPLY DISTURBING REPORTS"
Taliban and government officials have confirmed that the Islamists have overrun six provincial capitals in recent days in the north, west and south.
Security forces in Pul-e Khumri, capital of Baghlan province, to the southeast of Aibak, were surrounded as Taliban closed in on the town at a main junction on the road to Kabul, a security official said.
Gulam Bahauddin Jailani, head of the national disaster authority, told Reuters there was fighting in 25 of the 34 provinces and 60,000 families had been displaced over the past two months, with most seeking refuge in Kabul.
UN human rights chief Michelle Bachelet said the atrocious situation facing so many Afghans would deteriorate unless all parties returned to negotiations.
Her office said reports of violations that could amount to war crimes and crimes against humanity were emerging, including "deeply disturbing reports" of the summary execution of surrendering government troops.
"People rightly fear that a seizure of power by the Taliban will erase the human rights gains of the past two decades," she said.
The Taliban, ousted in the weeks after the Sep 11, 2001 attacks on the United States, are in a position to advance from different directions on Mazar-i-Sharif. Its fall would deal a devastating blow to Ghani's government.
Atta Mohammad Noor, a northern militia commander, vowed to fight to the end, saying there would be "resistance until the last drop of my blood".
"I prefer dying in dignity than dying in despair," he said on Twitter.
India was sending a flight to the city to take its citizens home, its embassy said, asking Indians to leave. The United States and Britain have already advised their citizens to leave Afghanistan.
The United States will complete the withdrawal of its forces at the end of this month under a deal with the Taliban, which included the withdrawal of foreign forces in exchange for Taliban promises to prevent Afghanistan being used for international terrorism.
The Taliban promised not to attack foreign forces as they withdraw but did not agree to a ceasefire with the government. Intermittent talks between the Afghan rivals have been fruitless.