NATO coalition forces have staged a daring nighttime raid, swooping in with helicopters, to free four humanitarian aid workers who were being held in a cave in a remote Afghan province. Five kidnappers were killed in the operation early Saturday.

The aid workers were kidnapped May 22 while traveling by horseback to treat villagers suffering from malnutrition in Badakhshan. They work for Medair — a Swiss-based humanitarian non-governmental organization.

Medair identified their workers as 28-year old Helen Johnston, who is British, and 26-year-old Moragwa Oirere, who is Kenyan. The group did not reveal the names of its two local Afghan staff who were also rescued, but said all its colleagues are safe and are being reunited with their families.

British forces took part in the operation, which was authorized by Prime Minister David Cameron. He described the rescue as “extraordinarily brave” and “breathtaking.” The rescue team did not suffer any casualties in the operation.

U.S. General John Allen, the top commander of U.S. and NATO forces in Afghanistan, said he is proud of the coalition forces that “planned, rehearsed, and successfully conducted” the rescue operation.

It was not immediately clear what demands the kidnappers had made.