Media reports on Friday said that the Taliban militants took control of the capital of Ghor province.
The Associated Press cited Fazil Haq Ehsan, the head of the provincial council in the central province of Ghor, as saying its capital, Feroz Koh, fell to the Taliban.
The militants also wrested control of the capitals of Zabul and Uruzgan provinces in the South.
Atta Jan Haqbayan, the provincial council chief in Zabul, said the local capital of Qalat was taken by the militants and that officials were in a nearby army camp preparing to leave.
According to Bismillah Jan Mohammad and Qudratullah Rahimi, lawmakers from Uruzgan, local officials surrendered Tirin Kot to the militant group.
Mohammad added that the governor was heading to the airport to leave for Kabul.
Earlier on Friday, reports said the Taliban seized Helmand's Lashkar Gah following weeks of clashes.
The Taliban have taken half of the country's 34 provincial capitals in recent days, including its second- and third-largest cities, Herat and Kandahar, which fell to the militants alongside Ghazni on Thursday.
After seizing Herat, the Taliban captured veteran Commander Mohammad Ismail Khan, who had been leading fighters against the militant group in recent weeks, an official said.
The official added that the militants had vowed not to harm him and other captured officials.
A spokesman for the militant group confirmed that Khan was in their custody.
More than two-thirds of the country are now under the control of the militants, who are tightening noose around the capital, Kabul.
A new US military assessment on Thursday said the Taliban could isolate Kabul in 30 days and potentially take it over in a few months.
As the Taliban advances on Kabul, NATO will hold an urgent meeting starting at 1300 GMT on Friday to discuss the deteriorating situation in Afghanistan, diplomatic and official sources told AFP.
The announcement came as the United States plans to send an additional 3,000 troops to Afghanistan to assist with the evacuation of US embassy staff and American citizens. Britain also said it would deploy around 600 troops to help its nationals and local translators leave the country.
AFP cited one source as saying the meeting would focus on evacuation planning from Afghanistan.
United Nations Secretary-General Antonio Guterres also called on Taliban militants to “immediately halt” their military campaign against government troops and return to the negotiating table in good faith “in the interest of Afghanistan, and its people”.
Speaking at a press conference at the UN headquarters in New York on Friday, Guterres said that humanitarian needs were “growing by the hour” as Afghanistan is largely spinning out of control.
“The message from the international community to those on the warpath must be clear: taking power through military force is a lost proposition. That can only lead to a protracted civil war or the complete isolation of Afghanistan,” he said.
The UN chief noted that more than 1,000 people have been killed or wounded from indiscriminate attacks by Taliban against civilians, notably in Helmand, Kandahar and Herat provinces, in just the past month.
“I call on all parties to take heed of the conflict's heavy toll and its devastating impact on civilians. They all must do more to protect civilians,” Guterres added.