The Taliban said Tuesday their forces had killed at least 40 fighters of an Afghan insurgent group led by the son of a late anti-Taliban commander during renewed fighting in the northern Panjshir province.
As a video apparently showing the carnage goes viral online, a government spokesman on Wednesday said they were "looking into" it.
The National Resistance Front (NRF), a nascent group operating mainly out of the Panjshir Valley, said the video showed some of its fighters being executed and accused the Taliban of "war crimes".
The video shows two groups of men squatting on a hillside with their hands tied behind their backs before being shot with automatic rifles by Taliban fighters.
The fighters can be heard shouting "Allahu Akbar", and a man is later heard saying "stop it, stop it" after the captives slump forward, apparently dead.
Checks by AFP's digital verification team show the first versions of the video only appeared online in the last 24 hours, and government spokesman Bilal Karimi said authorities were investigating.
"We are looking into it to know exactly when these videos were filmed and to know whether they are old," Karimi told AFP.
"But so far, we absolutely don't know about the place, timing of the videos, or who the people in them are."
The NRF said those shown being executed in the video were captured during fighting in the valley.
"The criminal Taliban... committed a war crime again by shooting & martyring eight" members of the NRF, the insurgent group's spokesman Sibghatullah Ahmadi said on Twitter.
The scenic Panjshir Valley is famed for being a site of Afghan resistance against Soviet forces in the 1980s and an anti-Taliban rebel base during the Islamists' first stint in power in the late 1990s.
The NRF were the last to hold out against the Taliban's takeover of the country in August last year by retreating to the valley.
NRF forces in May announced an offensive against the Taliban -- their first since the hardline Islamists seized power.
Scores of civilians had fled the valley in the initial bout of fighting, but there has been a lull in recent weeks.
However, fresh fighting erupted in the valley in the past few days, residents and the insurgent group said.
Government spokesman Zabihullah Mujahid said 40 NRF fighters, including three commanders, had been killed by Taliban forces.
"Sweeping clearance operations were conducted against the rebels in Rukha, Dara and Abshar district of Panjshir province," Mujahid said on Twitter, adding that another 101 insurgents had been arrested.
He did not say when the NRF fighters were actually killed.
NRF, though, on Tuesday said the Taliban was exaggerating the number of fighters killed.
"We refute the numbers. They have inflated the numbers," Ali Nazary, head of NRF's foreign relations, told AFP.
"Only a small group of our forces were captured and killed by the Taliban. Our forces fought fiercely till the last bullet."
NRF says its offensive would continue across 12 provinces where its forces have a presence, mostly in the north.
