A female British doctor is understood to be among at least 10 people murdered by gunmen in the far north of Afghanistan on Friday.
The group included eight foreigners – one of them a Briton – six Americans and a German working for a project run by a small Christian aid organisation called International Assistance Mission (IAM).
A Taliban spokesman claimed responsibility saying the attack was on "Christian missionaries" who were carrying bibles. It is possible the Taliban were simply exploiting early media reports about killings they in fact had nothing to do with.
A British doctor called Karen Woo was known to be on the expedition and played a major part in organising it, including by running fundraising events in London and Kabul to pay for the "Nuristan Medical Expedition 2010".
Woo, from London, had established an organisation called Bridge Afghanistan to help run medical projects in the country.
Writing on the expedition's Facebook page, Woo described herself as the team doctor and said she would run the mother and child clinics inside Nuristan. She wrote that the team also included an eye doctor and a dental surgeon.
According to IAM the group were returning from a several week long trip to provide basic health in a remote area of Nuristan province when they were attacked by gunmen in a forested area of Badakhshan, the most north-eastern of Afghanistan's provinces.
Their bullet-riddled bodies were discovered by local officials on Friday next to three shot-up vehicles.
Dirk Frans, the director of the Christian organisation, said IAM had last been contacted by the group via satellite phone on Wednesday.
In a short statement on its website, the organisation said the victims were likely working on the organisation's "eye camp team" project in Nuristan at the invitation of local communities and were returning to Kabul when they were attacked.
"At this stage we do not have many details but our thoughts and prayers are with the families and friends of those who are presumed killed. If these reports are confirmed we object to this senseless killing of people who have done nothing but serve the poor. Some of the foreigners have worked alongside the Afghan people for decades."
General Agha Noor Kemtuz, the local police chief, told the Observer they were having lunch in heavily forested area at around 2pm when around 10 gunmen arrived and took all their money before shooting them one by one.
"They had been warned by locals not to stay in the forest because it is not safe," he said.
He said the only surviving member of the party was an Afghan man called Safiullah whose life was saved after he desperately recited passages from the Koran as the gunmen were executing the other people.
General Kemtuz said there had been 11 people in the party including three Afghans and eight foreigners.
Whilst the US embassy confirmed it believed several Americans were among the dead, the British embassy was unable to confirm whether any British citizens were killed.
"We are aware of the reports and are actively investigating them with local authorities and others in country," a spokeswoman for the embassy said.
Woo described the trip into the remote area of Nuristan in gruelling terms, saying much of it would be done on foot and with pack horses, travelling 120 miles and climbing 16,000ft at one point.
"The expedition will require a lot of physical and mental resolve and will not be without risk but ultimately, I believe that the provision of medical treatment is of fundamental importance and that the effort is worth it in order to assist those that need it most," she wrote.
With local officials reporting that almost everything of value was removed from the vehicles, it is widely assumed that robbery was the main motivation for the attackers.
However, a spokesman for the Taliban told the Associated Press that the hardline insurgent movement killed the group because they were "preaching Christianity" and "spying for the Americans".
The NGO, which has been operating in Afghanistan since 1966, describes itself as a non-profit Christian organisation that works on health projects and economic development.
However, there are many such Christian aid organisations operating in Afghanistan all of whom take enormous care not to be seen to be proselytising or seeking to convert Afghans. Such allegations, including some in May against Norwegian Church Aid, can quickly stir up enormous public controversy.