Taliban insurgents captured the city of Ghazni, the ninth provincial capital they have seized in a week as US intelligence said the capital Kabul could fall to the insurgents within 90 days.
The speed of the Taliban advance has sparked widespread recriminations over US President Joe Biden's decision to withdraw US troops and leave the Afghan government to fight alone.
The Taliban control about two-thirds of Afghanistan, with the last of the US-led international forces set to leave by the end of the month, and their guerrilla army has waged war on multiple fronts, resulting in thousands of families fleeing the provinces in hope of finding safety in Kabul and other cities.
A senior security official said on Thursday the Taliban had captured Ghazni, which is on the highway between Kabul and the second city of Kandahar, and had occupied all of its government agency headquarters after heavy clashes.
"All local government officials, including the provincial governor, have been evacuated towards Kabul," said the official who declined to be identified.
Fighting has also been intense in the southern city of Kandahar. The city hospital had received scores of bodies of members of the armed forces and some wounded Taliban, a doctor said late on Wednesday.
The Taliban said they had captured Kandahar's provincial prison.
"Fighting did not stop until 4am and then after the first prayers it started up again," said an aid worker in Kandahar.
The Taliban also said they had seized airports outside the cities of Kunduz and Sheberghan in the north and Farah in the west, making it even more difficult to supply beleaguered government forces.
The Taliban said they had also captured the provincial headquarters in Lashkar Gah, the embattled capital of the southern province of Helmand, a hotbed of militant activity.
Government officials there were not immediately available for comment. Fighting had also flared in the northwestern province of Badghis, its governor said.
Bordering Pakistan, Kandahar and other southern and eastern provinces have long been Taliban heartlands but it has been in the north where they have made their biggest gains in recent weeks.
Even when the Taliban ruled the country they never controlled all of the north. This time, they appear to be determined to secure it fully before turning their attention to Kabul.
Government forces have withdrawn from hard-to-defend rural districts to focus on holding main population centres.
Desperate to stem the Taliban advance, President Ashraf Ghani flew to Mazar-i-Sharif to rally old warlords he had previously tried to sideline, now needing their support to defend the biggest city in the north as the enemy closed in.
In Washington, a U.S. defence official on Wednesday cited US intelligence as saying the Taliban could isolate Kabul in 30 days and possibly take it over within 90, following their recent rapid gains.
"But this is not a foregone conclusion," the official said, speaking to Reuters on condition of anonymity, adding that the Afghan security forces could reverse the momentum by putting up more resistance.
Biden said on Tuesday he did not regret his decision to withdraw and urged Afghan leaders to fight for their homeland.
All gateways to Kabul, which lies on a plain surrounded by mountains, were choked with civilians fleeing violence, a Western security source said, adding that there was a risk Taliban fighters could be among them.
The Taliban, who controlled most of Afghanistan from 1996 to 2001, when they were ousted for harbouring al-Qaeda chief Osama bin Laden after Sept. 11, wants to defeat the US-backed government and reimpose strict Islamic law.
Australian Associated Press
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