Afghan resistance movement and anti-Taliban forces conduct military training at the Malimah area of Dara district in Panjshir province on September 2.
CNN  — 

Fighting in Afghanistan’s last major holdout against Taliban rule continued through Friday after heavy clashes erupted overnight between Taliban fighters and an anti-Taliban group, according to Taliban sources.

Panjshir Valley, a mountainous, inaccessible region north of Kabul, has a long history of resisting the insurgent group. In the late 1990s, it was a center of resistance against the Taliban during their rule.

Now the National Resistance Front (NRF), a multi-ethnic group that includes former Afghan security force members and reportedly numbers in the thousands, has continued the fight against the Taliban following the militants’ almost-complete takeover of Afghanistan.

Sporadic fighting between the NRF and the Taliban has continued for two weeks now. The Taliban have been massing forces in and around Panjshir province in recent weeks, and said on Monday they had captured three districts in the valley.

An NRF commander in Panjshir Valley said fighting was taking place around the Shatal district of Panjshir. The commander said NRF forces had inflicted hundreds of casualties on the Taliban. The Taliban denied these claims.

A Taliban source said the militants attacked Panjshir from multiple directions, including from nearby Parwan province and the northern Badakhshan region.

CNN has been unable to independently verify the overall casualty figures in the latest round of fighting, which also flared in provinces neighboring the Panjshir valley. Taliban video reviewed by CNN appeared to show its fighters in a gorge in the Shatal region, on the southwestern end of the valley.

The NRF commander claims the Taliban threatened civilians and took hostages, warning residents they can be killed for supporting the resistance.

Anti-Taliban forces take part in military training in the Panjshir Valley, the last major holdout against Taliban rule, on Thursday.

Amrullah Saleh, a former Afghan vice president who joined the anti-Taliban fight, claimed on Twitter the Taliban “blocked humanitarian access to Panjshir” and forced military-aged men to walk minefields to clear them.

The Taliban “have shut phone, electricity and [are] not allow[ing] medicine either,” Saleh said.

In official statements, the Taliban said they seek a negotiated end to the fighting and want Panjshiris to live in peace, highlighting their offers of amnesty to forces once aligned with the country’s former US-backed government.

Former Afghan President Hamid Karzai, who remains in Afghanistan, called on both sides to end the fighting.

“Unfortunately, in recent days, despite the efforts of the reformers, military operations and fighting have started in Panjshir, which is a matter of deep concern and I do not consider the consequences to be in the interest of the country and the people,” Karzai said in a statement. “That is why I call on both sides that war is not the solution for an Afghanistan that is wounded and suffering.”

Epicenter of guerilla warfare

The overnight clashes between the Taliban and the NRF started late Thursday, and were very intense, said an NRF source. “They (Taliban) are using their last power to get in, but clashes are still ongoing,” the source added.

The anti-Taliban forces in Panjshir Valley includes  local resistance forces as well as remnants of the former Afghan army.

Earlier on Thursday, Fahim Dashti, an NRF spokesperson, said in an audio message that the Taliban lost 40 of their forces in their ongoing attempts to enter Panjshir. Ali Nazary, another spokesperson from the group, said Thursday that the Taliban had also lost a number of heavy equipment and weaponry that had been destroyed.

CNN has not independently verified the Taliban casualties.

Separately, a Taliban source provided videos purportedly of fighting and the aftermath. CNN could not immediately verify the location or when the videos were filmed.

Anti-Taliban fighters patrol the Anaba District of Afghanistan's Panjshir province on September 1.

The Panjshir Valley is the epicenter of Afghan guerrilla warfare, and has long withstood foreign occupation, from the British Empire’s army to Soviet forces and the Taliban.

The rugged, inaccessible landscape plays a part in its defensive success, giving local forces an advantage over would-be invaders.

After the USSR, which controlled Kabul and large swaths of the country in the 1980s, withdrew from Afghanistan in 1989, various factions of mujahedeen – or Islamic holy warriors – split into groups, fighting for control of the country.

The Northern Alliance – now a main component of the NRF – was soon formed. Led by Ahmad Shah Massoud, the group managed to keep the Panjshir Valley free of Taliban influence. Massoud led an anti-Taliban offensive until he was assassinated by al Qaeda operatives two days before the September 11, 2001 attacks.

The coalition, and the broader NRF, is now led by Massoud’s son, Ahmad Massoud, who has vowed to continue the fight against the Taliban in the wake of their near takeover of Afghanistan. Massoud and the NRF are now gathering anti-Taliban forces in the Panjshir Valley, which include local resistance forces as well as remnants of the former Afghan army.

People fleeing the Taliban, including the former Afghan Vice President, Amrullah Saleh, have also sought refuge in the Valley.

“The Taliban have not changed, and they still are after dominance throughout the country,” Massoud told CNN in an interview on Wednesday. “We are resisting dominance, intolerance, and oppression brought by one political force over the majority of the population that do not support them.”

He added that he and the NRF were still trying to negotiate with the Taliban – but so far, that dialogue “hasn’t resulted in anything tangible.” Talks have been taking place in the city of Charika, the capital of the neighboring Parwan province.

“Negotiations have their limits,” he said, quoting a prominent Prussian military general. “War is the continuation of politics, and if we face aggression we will be forced to fight and launch resistance to defend our land, people, and values.”