(CNN) -- U.S. officials issued scathing condemnation Sunday of an attack on 10 multinational medical aid workers in Afghanistan as the victims' bodies were returned to Kabul.

The Taliban has claimed responsibility for the Thursday attack, said Karl Eikenberry, U.S. ambassador in Afghanistan, but "we do not know whether they are responsible or simply taking credit for the cowardly and despicable acts of others."

Six Americans, two Afghans, a Briton and a German were shot and killed by gunmen in Badakhshan, a remote northeastern region of the country, said Dirk Frans, the director of the International Assistance Mission. Two other Afghans on the team were alive, Frans said.

Eikenberry said officials were working to identify the victims.

Thomas Grams of Durango, Colorado, was among the Americans who died, Katy Shaw, an administrator with Global Dental Relief, said Sunday. Grams had been working with the group for 10 years, she said, and had been to Afghanistan several times, along with Nepal. He was a general dentist who gave up his private practice to do relief work, she said. Grams started as a volunteer with the group, which provides dental care for impoverished children, but later became a team leader.

"He was one of our favorites," Shaw said, describing Grams as quiet, unassuming and modest.

Libby Little, the wife of American optometrist Tom Little, told CNN Saturday her husband was killed, and the British Foreign Office confirmed the death of Dr. Karen Woo on Sunday.

The bodies of the 10 were retrieved and returned to Kabul by helicopter on Sunday, said U.S. embassy spokeswoman Caitlin Hayden.

"The Taliban has called this group of medical aid workers spies and proselytizers," Eikenberry said in a video statement. "They were no such thing. These were selfless volunteers who devoted themselves to providing free and much-needed health care to Afghans in the most remote and difficult parts of your country.

"Their murder demonstrates the absolute disregard that terrorist-inspired Taliban and other insurgents have for your health, have for your security and have for your opportunity," Eikenberry said, apparently speaking to the Afghan people. "They don't care about your future. They only care about themselves and their own ideology."

Aqa Nwor Kentoz, the police chief in the province, says the gunmen stopped the group on the road, took their belongings and shot them one by one. An Afghan was released because he was reciting excerpts from the Quran, Kentoz said.

The team had spent several days in Nuristan province, where they treated cataracts and other eye conditions, U.S. Secretary of State Hillary Clinton said in a statement.

"At their next stop, they planned to run a dental clinic and offer maternal and infant health care," Clinton said. "They were unarmed. They were not being paid for their services. They had traveled to this distant part of the world because they wanted to help people in need. They were guests of the Afghan people. The Taliban stopped them on a remote road on their journey from Nuristan, led them into a forest, robbed them and killed them."

"We are heartbroken by the loss of these heroic, generous people," Clinton said. "We condemn in the strongest possible terms this senseless act. We also condemn the Taliban's transparent attempt to justify the unjustifiable by making false accusations about their activities in Afghanistan."

Badakhshan, bordered by Tajikistan to the north and Pakistan to the south, is a sparsely populated region comprised of a majority Tajik population and an Uzbek and Kyrgyz minority. Badakhshan was the only province that was not controlled by the Taliban when it ruled Afghanistan.