Afghanistan has replaced its army chief, as Taliban militants continue to make rapid advances.
Insurgents have taken control of 10 of the country’s 34 provincial capitals.
On Thursday the Taliban said they had taken the strategically important Ghazni city, which is on the road to the national capital Kabul.
President Ashraf Ghani earlier flew to the northern city of Mazar-i-Sharif – traditionally an anti-Taliban bastion – to try to rally pro-government forces.
The removal of the country’s army chief, General Wali Mohammad Ahmadzai, was confirmed to the BBC on Wednesday. He had only been in the post since June.
His successor will have to deal with escalating violence across the country, as the Taliban continue their offensive. US and other foreign troops have all but withdrawn following 20 years of military operations.
More than 1,000 civilians have been killed in Afghanistan in the past month, according to the UN.
Also on Wednesday, President Ghani held crisis talks in Mazar-i-Sharif with ethnic Uzbek warlord Abdul Rashid Dostum and prominent ethnic Tajik leader Atta Mohammad Noor about defending the city.
Mr Dostum, a veteran commander, was quoted as saying: “The Taliban have come to the north several times but they were always trapped.”
For years, Mr Ghani tried to sideline the warlords in an attempt to boost the Afghan National Army, and now he is turning to them in his hour of need, the BBC’s Ethirajan Anbarasan says. Earlier this week, the president also agreed to arm pro-government militia.
Mazar-i-Sharif lies close to the borders with Uzbekistan and Tajikistan, and its loss would mark the complete collapse of the government’s control over the north of Afghanistan.
In Kunduz, another northern provincial capital, hundreds of government soldiers – who had earlier retreated to the airport after the Taliban overran the city – have now surrendered.
According to local media reports, the Taliban have now taken over Kunduz airport and the army corps stationed there have surrendered.
Local sources told the BBC that fighting was also raging in eastern Afghanistan’s Ghazni on Wednesday, after Taliban insurgents entered the city centre.
The International Committee of the Red Cross (ICRC) humanitarian group later said intense “street-by-street” fighting was taking place in Afghanistan’s second-largest city Kandahar.
The Taliban claimed to have taken over the city’s prison, though this has not been confirmed.
According to one US official speaking to CBS News, Afghanistan’s capital could fall to the Taliban in as soon as 90 days.
However, the official told news agency Reuters that it was possible for the Afghan security forces to halt the Taliban’s momentum by putting up more resistance, adding that the fall of Kabul was not a “foregone conclusion”.
The official, who spoke on condition of anonymity, was reportedly citing US intelligence.
In the city of Lashkar Gah, in Helmand province, ICRC director-general Robert Mardini said hospitals were “struggling to deal with the dead bodies”.
In addition to fighting on the ground, US and Afghan planes have been carrying out air strikes against Taliban positions in the country.
The Washington Post newspaper on Wednesday cited unnamed officials as saying the capital Kabul could fall to the Taliban within 90 days, based on US military assessments.
A senior adviser to Mr Ghani, Waheed Omer, dismissed this prediction. “It’s hard times for us but we know that we will prevail,” he told the BBC.
“They have managed to gain some territory but it’s not about territory. It’s about the people. The people don’t want them and they will soon find that it was a mistake to actually attack our people,” he said.
Psychological blow could be huge
Analysis by Inayatulhaq Yasini, BBC Kabul bureau editor
Mazar-i-Sharif, now a major economic centre, has historically been the supply gateway from the former Soviet Union to the country.
The government in Kabul recognises the importance of the city, and that is why the Afghan president visited it to hold talks with local leaders and former warlords.
The last time the Taliban took the city was in the 1990s. This happened without any heavy resistance after a deal was done with a rival of Abdul Rashid Dostum.
But now he is one of the key leaders fighting the militant group.
With violence surging, thousands of people have been fleeing in search of safety.
“We have no money to buy bread, or get some medicine for my child,” a 35-year-old street vendor who fled Kunduz province after the Taliban set fire to his home told the BBC.
“We had a good life, but because of the bomb blasts we lost our home”, a woman who fled the city of Pul-e-Khumri said.
Afghan politician Shukria Barakzai said the Taliban gains were “a red signal for the entire globe”.