Twelve were from the Royal Air Force, one was a Royal Marine and the last was a British army soldier, a spokesman said.
The Nato aircraft came down in Kandahar province in southern Afghanistan due to a technical problem, a spokesman for the alliance in Kabul said earlier, stressing it was not shot down.
In a statement, Britain's Defence Secretary Des Browne said: "This is dreadful and shocking news.
"I know that the people of Britain will join me in sending our deep condolences to the loved ones of those who have lost their lives, and to the British military as it deals with the loss of friends and comrades."
The latest deaths — the greatest loss of British life in Afghanistan in a single incident — come just a day after a Fijian British Army soldier died fighting Taliban militants in the volatile Helmand province on Friday.
The Ministry of Defence in London immediately set up a special incident line for concerned family members. Browne stressed it was "not the time for speculation" and work was ongoing to secure the crash site.
"Everyone will understand that our first priority is to inform and support the families of those on board," he added.
"I can say, however, at this stage all the indications are that this was a terrible accident and not the result of hostile action.
Güncelleme Tarihi: 20 Eylül 2018, 18:16