The Taliban said they have taken control of Panjshir province north of Kabul, the last holdout of anti-Taliban forces in the country and the only province the Taliban had not seized during last month's blitz across Afghanistan.
Thousands of Taliban fighters overran eight districts of Panjshir overnight, according to witnesses in the area who spoke on condition of anonymity, fearing for their safety.
Taliban spokesman Zabihullah Mujahid issued a statement, saying Panjshir was now under the control of Taliban fighters.
The anti-Taliban forces had been led by the former vice president, Amrullah Saleh, and also the son of the anti-Taliban fighter Ahmad Shah Massoud who was killed just days before the 9/11 terrorist attacks in the United States.
Nestled in the towering Hindu Kush mountains, the Panjshir Valley has a single narrow entrance.
Local fighters held off the Soviets there in the 1980s and also the Taliban a decade later under the leadership of Massoud.
Mr Massoud's son Ahmad had issued a statement on Sunday, calling for an end to the fighting of recent days.
Watch: Panjshir Valley: Afghanistan's last stand against the Taliban.
The young British-schooled Mr Massoud said his forces were ready to lay down their weapons but only if the Taliban agreed to end their assault.
Late on Sunday dozens of vehicles loaded with Taliban were seen swarming into Panjshir Valley.
There has been no statement from Mr Saleh, Afghanistan’s former vice president who had declared himself the acting president after President Ashraf Ghani fled the country on 15 August as the Taliban reached the gates of the capital.
The Taliban entered the presidency building that day.
In his statement, Mr Mujahid sought to assure residents of Panjshir that they would be safe — even as scores of families reportedly fled into the mountains ahead of the Taliban's arrival.
"We give full confidence to the honourable people of Panjshir that they will not be subjected to any discrimination, that all are our brothers, and that we will serve a country and a common goal," Mr Mujahid said in his statement.
The Taliban had stepped up its assault on Panjshir on Sunday, tweeting that their forces had overrun Rokha district, one of the largest of eight districts in the province.
Several Taliban delegations attempted to negotiate with Rokha's holdouts, but talks failed to gain traction.
Fahim Dashti, the spokesman for the anti-Taliban group, was killed in a battle on Sunday, according to the group's Twitter account.
Mr Dashti was the voice of the group and a prominent media personality during previous governments.
He was also the nephew of Abdullah Abdullah, a senior official of the former government who is involved in negotiations with the Taliban on the future of Afghanistan.
Meanwhile, at least four planes chartered to evacuate several hundred people seeking to escape the Taliban's takeover of Afghanistan have been unable to leave the country for days, officials said on Sunday.
There have been conflicting accounts about why the flights weren't able to take off, as pressure ramps up on the US to rescue those left behind.
An Afghan official at the airport in the northern city of Mazar-e-Sharif said that the would-be passengers were Afghans, many of whom did not have passports or visas, and thus were unable to leave the country.
He said they had left the airport while the situation was sorted out.
Watch: Afghanistan veteran 'very happy with the sacrifices' made in the country despite the return of the Taliban.
The top Republican on the US House Foreign Affairs Committee, however, said that the group included Americans and they were sitting on the planes, but the Taliban were not letting them take off, effectively "holding them hostage".
He did not say where that information came from.
It was not immediately possible to reconcile the accounts.
The final days of the US' 20-year war in Afghanistan were marked by a harrowing airlift at Kabul's airport to evacuate tens of thousands of people, Americans and their allies, who feared what the future would hold, given the Taliban's history of repression, particularly of women.
When the last troops pulled out on 30 August, though, many were left behind.
The US promised to continue working with the new Taliban rulers to help those who want to leave, and the militants pledged to allow anyone with legal documents to depart.
But Representative Michael McCaul of Texas told Fox News on Sunday that US citizens and Afghan interpreters were being kept on six planes.
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Cover image: File photo of the Panjshir Valley in eastern Afghanistan (Picture: Maurice Brand/Alamy).