The aircraft involved in the accident was a Royal Air Force Nimrod MR2 based at RAF Kinloss in Scotland. It was lost supporting an International Security Assistance Force (ISAF) mission.
The Commander of British Forces in Afghanistan, Brigadier Ed Butler, said:
"Over the last few days we have experienced a number of incidents which have resulted in the tragic loss of life and injury to UK personnel serving in Afghanistan.
"This has clearly caused profound personal devastation for the families, friends and colleagues of those who have made such a sacrifice and our thoughts and prayers are with all those involved.
"Notwithstanding today’s accident, and other losses suffered so far, the resilience, morale, and bearing of our servicemen and women is quite remarkable.
"I am personally humbled by their courage and commitment in getting on with the tough job in hand; delivering over and above, and making a difference to the ordinary people of Afghanistan."
On learning of the incident, Secretary of State for Defence 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.
"This is not the time for speculation, as the operation to secure the crash site is ongoing. We will provide further information as soon as there is more to say.
"Everyone will understand that our first priority is to inform and support the families of those on board.
"I can say, however, at this stage all the indications are that this was a terrible accident and not the result of hostile action.
"This tragic incident should serve to remind us all of the risks the British military shoulder on all our behalf across the world every day."
Britain’s most senior Royal Air Force officer, Chief of the Air Staff, Air Chief Marshal Sir Glenn Torpy, added:
"The loss of the Nimrod MR2 over Afghanistan earlier today is desperately sad and tragic news. Our thoughts are very much with the families and loved ones of the brave and committed aircrew who lost their lives today, and our priority is to provide them all with the support they require at this extremely difficult time.
"As the Secretary of State has said, at the moment there is no reason to believe that the aircraft was lost as a result of hostile action. A Board of Inquiry has been convened to determine the cause of this tragic loss."
The media are asked to respect the wishes of service personnel and their families at Kinloss that they are not approached by the media at this very difficult time.
We are currently in the process of informing the next of kin. Further details will be released when this process is complete.
Families who are concerned that their relatives may have been involved in this incident can call a special incident line set up by the MOD on 08457 800 900.