An investigation is under way to determine why a Lynx helicopter crashed in southern Afghanistan, killing five service personnel.
Investigators from the Military Aviation Authority have cordoned off the crash site near Kandahar and will inspect the wreckage of the light utility aircraft.
The MoD has denied claims by the Taliban that insurgents shot down the helicopter, saying initial investigations indicated a technical problem during the routine flight rather than enemy action.
The inquiry is likely to look at the aircraft's log books and other documentation, in addition to weather conditions and whether the helicopter was carrying out an authorised job according to its capabilities, experts said.
It is not thought that other Lynx helicopters in use in Afghanistan will be immediately grounded following the crash.
A spokeswoman said: "The investigation is now under way, and the area of the crash has been cordoned off.
"We cannot go into further details. At this stage it is not known how long the investigation might last or when investigators will deliver their report, but it will be a thorough inquiry."
Three of the servicemen who died were from the Army Air Corps, based at RAF Odiham in Hampshire.
Prince Harry served as an Apache helicopter commander with the Army Air Corps during his tour of duty in Afghanistan last year.
A Royal Air Force serviceman stationed at the same base also died, along with a member of the Army Reserve from 3 Military Intelligence Battalion, based in London.
The next of kin of all five servicemen have been informed of their deaths but none has yet been named.
It is the third biggest single loss of life of British troops since the conflict in Afghanistan began in 2001, and brings the total number of UK service personnel killed there to 453.
David Cameron last night paid tribute to those who died, saying: "My heart goes out to the families and friends of those killed in this terrible tragedy.
"Every British fatality is a source of deep sadness. This latest incident, which has cost the lives of five UK service personnel, brings home to us all once again how our armed forces continue to put their lives on the line to help the people of Afghanistan.
"I cannot pay high enough tribute to each and every one of them for the job that they do and the sacrifices that they make."
The aircraft, believed to be a Westland Lynx Mk 9 helicopter, went down yesterday morning in the Takhta Pul district of Kandahar, some 30 miles from the Pakistan border.
Lynx helicopters are used for a wide range of roles, including transport, surveillance, resupply and operational support.
They are seen as "work horses" and carry a crew of three, including a pilot, co-pilot and gunner.
It is believed that the other two military personnel on board may have been travelling as passengers.
Defence analyst Paul Beaver said: "It is difficult to speculate on what has happened, but it sounds like this was a flying accident instead of a case of the aircraft being shot down.
"It could be weather related, it could be dust or it could have been trying to avoid birds, for example, or it could be some kind of mechanical failure. There is a whole range of possible causes."
Labour leader Ed Miliband said people across the UK would be saddened by the news, calling it "a tragic and poignant reminder of the sacrifices made by our armed forces in serving our country with bravery and distinction".
Major General Richard Felton, above, Commander Joint Helicopter Command, said: "It is with great sadness that we must confirm that five UK service personnel have been killed in this incident which, at this early stage, would appear to have been a tragic accident.
"Events like this, whilst mercifully rare, remind us of the risks our personnel face in their work in Afghanistan as we approach the conclusion of the combat mission later this year.
"Our thoughts are with the families and loved ones of those who have lost their lives."
The crash is the worst incident involving a British military helicopter in Afghanistan since the war began there more than 12 years ago.
Previously, three Chinook crashes and one Apache emergency landing left no fatal victims, according to reports.
In September 2006 a Nimrod surveillance aircraft from RAF Kinloss in Scotland exploded in mid-air near Kandahar, killing all 14 servicemen on board, while in March 2012 six soldiers died when their Warrior armoured fighting vehicle was hit by an improvised explosive device in Helmand Province.
Yesterday's incident equals the previous worst disaster involving a British helicopter, when a Lynx aircraft crashed in Basra City, Iraq, in May 2006 killing the five service personnel on board.
The deadliest single incident for US troops came in August 2011, when the Taliban shot down an American Chinook helicopter near Kabul, killing 30 Americans and eight Afghans.
Nato forces are currently preparing to withdraw combat troops by the end of this year, with responsibility for fighting the Taliban uprising handed over to the Afghan army and police.
So far this year, 23 Nato troops are thought to have been killed in Afghanistan.