Four workers with Swiss-based Medair, including a British woman, are freed after a night-time raid in Badakhshan province

This article is more than 8 years old

This article is more than 8 years old

British and American special forces have rescued four aid workers, including a 28-year-old British woman, in a daring night-time raid on a mountain cave in remote north-west Afghanistan.

The group, all employees of Swiss-based Medair, were abducted while travelling by donkey to flood-stricken areas of northern Badakhshan province on 22 May.

Their captors were armed with heavy machine guns, AK-47 assault rifles and rocket-propelled grenades. They moved the hostages from cave to cave in an area known locally as "ant valley" in a bid to avoid detection, Afghan officials said.

The Briton is Helen Johnston, a nutritionist who lived in Stoke Newington, north London, and studied at the London School of Hygiene and Tropical Medicine before her posting to Badakhshan.

"We are delighted and hugely relieved by the wonderful news that Helen and all her colleagues have been freed," her family said in a statement, which also thanked the rescuers and asked for privacy at a "special time".

Helen Johnston, the rescued British aid worker. Photograph: PA

The other hostages were the 26-year-old Kenyan Moragwa Oirere and two Afghans who were not named. A fifth hostage escaped shortly after the group were captured.

The operation to free the group, authorised by the British prime minister, David Cameron, and the commander of Nato and US forces in Afghanistan, General John Allen, began at around 1.30am. An hour later all four were free.

Cameron said decisions on rescue attempts were "extraordinarily difficult" and "never rushed into", but he decided the risks to the hostages' lives were getting greater, the Press Association reported.

Their captors were a mix of insurgent sympathisers, narco-traffickers and common criminals, according the governor of Badakhshan province.

"One part had a connection with the Taliban, and some of them were drug smugglers … others of the group were criminals," the governor, Shah Waliullah Adeb, told the Guardian.

"They kept them in seven different places in the mountain caves, where there are no local residents, to avoid the security forces finding their hiding place."

The abductors had told local elders who tried to negotiate a release that they wanted a $4m ransom and the release of a notorious local criminal, he added.

Johnston told the Evening Standard last November that life was "gruelling" and physically tough in the remote region, but widespread malnutrition made their work essential.

"It can be frustrating and hard, but there is no doubt that there is a fundamental need for us to be here. Too many children are suffering for us not to be," she was quoted saying.

Medair said it had been bolstered by support from Afghans it served, but declined to comment on whether it was reassessing its presence in Afghanistan after the kidnapping.

"We are immensely grateful to all parties involved in ensuring their swift and safe return," said a Medair spokesperson, Aurélien Demaurex. "We are also very grateful for the overwhelming messages of support from local Afghan communities."

Kidnapping has been a risk for foreigners working in Afghanistan for many years. The British aid worker Linda Norgrove was killed during a rescue attempt that went wrong in October 2010.

And violence and instability have been spreading to areas of the country such as Badakhshan that were once considered relatively safe. Also in 2010, 10 foreign medical workers, including six Americans, were killed in Badakhshan in an attack blamed on insurgents.

Afghan forces have taken over security in the provincial capital, Faizabad, and some other parts of Badakhshan before the withdrawal of western combat forces in 2014.