Kabul, Afghanistan ? A Christian charity said Monday it had no plans to leave Afghanistan despite the brutal murders last week of 10 members of its medical aid team, six of them Americans.

Police were holding the lone Afghan survivor for questioning, insisting he is not a suspect although authorities have lingering questions about his account of the horrific massacre in northern Afghanistan.

The attack, far from the main theaters of the war in the east and south, underscored the growing insecurity in the region.

It was also the biggest assault on foreign Christians since the 2007 kidnapping of 23 South Korean missionaries by the Taliban in Ghazni province. Two male hostages were slain before the South Korean government negotiated their release the following month.

The survivor of last week’s attack, a driver named Saifullah who had worked for the humanitarian group for four years, was flown to Kabul on Sunday from Badakhshan province. Also taken to the capital were the bodies of the six Americans, two Afghans, a Briton and a German who were gunned down after finishing a two-week medical mission treating Afghan villagers in the remote Parun valley of Nuristan province.

The Taliban claimed responsibility for the Thursday murders, alleging that the group, most of them devout Christians, were spies and tried to convert Muslims. Some local officials suspect common criminals carried out the attack.

U.S. Embassy spokeswoman Caitlin Hayden said the FBI has opened an investigation into the deaths in cooperation with Afghan authorities.

During a press conference Monday, Dirk Frans, the director of the International Assistance Mission that organized the trip, insisted that conversion was not the aim of the trip and that the Afghan government had given them permission to treat Afghans in the area.

He said the IAM had made no secret that it was a Christian organization during its four decades in Afghanistan and was legally registered with the Afghan government.

“Our faith motivates and inspires us, but we do not proselytize,” he said. “We abide by the laws of Afghanistan” that make proselytizing illegal.

Frans said “as things stand right now” his organization has no plans to leave Afghanistan, having operated here during the Soviet occupation of the 1990s, the civil war of the 1990s and during five years of Taliban rule.

But Frans acknowledged that the losses left the organization “devastated.”

Team leader Tom Little, 62, of Delmar, N.Y., and Dan Terry, 64, had worked in Afghanistan for more than 30 years and had raised families here. As a sign of the group’s commitment to this country, Frans said the families of five of the eight foreigners had chosen to bury their relatives in Afghanistan.

Frans said he had asked Little why there weren’t more Afghans and fewer foreigners on the mission. Frans quoted Little as saying such missions needed to be spearheaded by “committed expatriates” and that the Afghans would take over later.

The three other Americans were Brian Carderelli, 25, of Harrisonburg, Va., the videographer for the mission; Cheryl Beckett, 32, of Knoxville, Tenn., an expert in nutritional gardening and mother-child health; Dr. Tom Grams, 51, of Durango, Colo., a dentist; and Glen Lapp, a nurse from Lancaster, Pa.