At least 10 mine clearers working for Halo Trust in Afghanistan’s northern province of Baghlan have been shot dead, and more than a dozen wounded.
Afghan officials blamed the Taliban, saying militants “started shooting everyone” in the compound.
But Halo Trust CEO James Cowan told the BBC that “the local Taliban… came to our aid and scared the assailants off”. The Taliban has also denied the attack.
Violence has surged as the US began to withdraw its last troops on 1 May.
The departure of international troops comes amid deadlock in peace talks between the Afghan government and the Taliban.
Several districts in Baghlan province have seen fierce fighting between the Taliban and government forces.
The workers were killed when masked gunmen burst into their compound at 21:50 (17:20 GMT) on Tuesday, after they had spent a day removing mines from a nearby field.
Interior Ministry spokesman Tareq Arian told reporters that “the Taliban entered a compound of a mine-clearing agency… and started shooting everyone”.
But the Taliban issued a swift denial.
“We condemn attacks on the defenceless and view it as brutality,” the militant group’s spokesman Zabihullah Mujahid tweeted. “We have normal relations with NGOs. Our Mujahideen will never carry out such brutal attacks.”
Mr Cowan of the Halo Trust told BBC Radio 4’s Today programme that the attackers went “bed to bed” shooting the workers “in cold blood” – but that the local Taliban helped the deminers.
“I think it’s important to know that the Taliban have denied responsibility for this, and indeed the local Taliban group came to our aid and scared the assailants off,” he said.
“We don’t know who the assailants were – we could speculate about, that but I won’t – but I think we have the capacity as the Halo Trust to operate on both sides of the line in this awful conflict,” he added.
In a clip police in Baghlan shared with reporters, a survivor of the attack said the gunmen asked if any of them were from the Hazara minority community before opening fire.
“Five to six armed men came, they took us to a room,” he said. “First they took all our money and mobile phones, and then they asked who our leader was.
They asked, ‘Is any Hazara here among you?’ We told them, ‘We don’t have any Hazara here.'”
He added that he was shot in the head, but managed to escape through a window.
Hazaras, Afghanistan’s third-largest ethnic group, have faced long-term discrimination and persecution, primarily because of their Shia faith.
In recent years, they have faced abductions and killings at the hands of both the Islamic State group and the Taliban.
The UK-based Halo Trust was founded in 1988 to remove ordnance left behind from the almost decade-long Soviet occupation of Afghanistan.
It was supported by Princess Diana, as well as by her son Prince Harry.