KABUL, June 2: Nato forces swooped in by helicopter before dawn on Saturday to rescue two female foreign aid workers and their two Afghan colleagues who were held by militants for nearly two weeks in a cave in northern Afghanistan.

British Prime Minister David Cameron hailed the “breathtaking” operation, which he approved on Friday afternoon after becoming increasingly concerned about the safety of the hostages, one of whom, 28-year-old Helen Johnston, was British.

Johnston was kidnapped along with Moragwa Oirere, a 26-year-old Kenyan, and the two Afghans while visiting aid sites in Badakhshan province on May 22. The four work for Medair, a humanitarian non-governmental organisation based near Lausanne, Switzerland.

The rescue operation was carried out by British troops in cooperation with other Nato and Afghan forces, Cameron told reporters outside 10 Downing Street in London. He said it was “extraordinarily difficult” to decide to go ahead with the operation, which involved a “long route march” without being discovered.

“It was an extraordinarily brave, breathtaking even, operation that our troops had to carry out,” said Cameron. “We will never be able to publish their names but the whole country should know we have an extraordinary group of people who work for us who do amazingly brave things.”

All four hostages were rescued safely, no British troops were injured and a number of Taliban militants and kidnappers were killed, said Cameron.

Past rescue attempts in Afghanistan have not always gone so well. In 2009, an Afghan translator kidnapped with a New York Times reporter was killed in a hail of bullets during a rescue attempt by British commandos.

In 2010, the US Navy's SEAL Team 6 tried to rescue Linda Norgrove, a Scottish aid worker, from her Taliban captors in Afghanistan. She was killed by a grenade thrown in haste by one of the American commandos.

Afghan officials said seven militants were killed during Saturday’s operation, which was launched around 1am.

Lt Col Jimmie Cummings, a coalition spokesman, said a helicopter rescue team reached the scene before dawn and confirmed that the hostages were there.

“The kidnappers were armed with heavy machine guns, rocket-propelled grenades and AK-47s,” Cummings said. “They were kidnapped by an armed terrorist group with ties to the Taliban.” The aid workers appeared to be in good health, but they will be evaluated before being reunited with their families, he said.—AP