Taliban spokesman Zabibullah Mujahid said on Monday the group had taken control of Panjshir province, albeit to face immediate disagreement from the rebels in the region.
Resistance fighters in Panjshir are or were the last major group contesting Taliban forces since they swept across most of the country over the last three weeks.
The resistance forces have banded together under the so-called National Resistance Front of Afghanistan (NRFA).
Mujahid also told reporters at a press conference in capital city Kabul that the "Afghan forces were trained in the past 20 years will be asked to rejoin the security department alongside Taliban members." He added that any insurgency against their rule would be "hit hard."
Both Taliban and resistance forces claim control over Panjshir
The NRFA said their fighters were "present in all strategic positions across the Panjshir Valley" and would continue the fight on Monday.
The NRFA is led by former Vice President Amrullah Saleh and Ahmad Massoud, the son of renowned anti-Taliban fighter Ahmad Shah Massoud who was killed in a suicide bombing just days before the 9/11 attacks. Massoud is likely to comment on the situation soon.
Massoud issued a statement on Sunday and said that their fighters were ready to lay down their weapons only if the Taliban agreed to halt their advances into the province.
The Taliban reportedly entered the valley late on Sunday night, according to the Associated Press news agency. Thousands of fighters overran eight districts of Panjshir on the intervening night between Sunday and Monday, AP reported citing witnesses from the area.
Taliban claims Panjshir province on several occasions
Three Taliban sources told Reuters news agency on September 3 they had taken full control of Afghanistan, including the Panjshir Valley. Several pro-Taliban Twitter accounts aired video clips purporting to show that the new rulers had captured tanks and other heavy military equipment inside the valley.
Heavy celebratory gunfire was heard in Kabul the same night.
Taliban spokesman Bilal Karimi said two districts of the province — Khink, Anabah — had fallen on September 4. He wrote that the "Mujahideen (Taliban fighters) are advancing toward the centre (of the province)" on Twitter.
Italian aid agency Emergency said that the Taliban had taken the village of Anabah on September 4. It said it was treating a "small number of wounded" in a statement.
Karimi said on September 5 that the provincial capital, Bazark, had fallen. The statement could not be verified. He posted an image of Taliban members standing in front of the gate of the Panjshir provincial governor's compound on September 6, after the Taliban claimed control of the province.
What is the importance of Panjshir?
Panjshir held out for nearly a decade against the Soviet Union's occupation in the 1980s and also the Taliban's first rule from 1996-2001.
"We will never give up the fight for God, freedom and justice," Massoud wrote on Facebook on September 4. This followed earlier unverified reports, not uncommon in recent days, that the Taliban had taken full control.
The NRFA had said in August that the Taliban "propaganda machine" was trying to spread distracting messages and that it had pushed Taliban forces back from another part of the valley.