It is thought a Patriot missile hit the plane
Two RAF Tornado jet crew members have been confirmed dead after being shot down by a US Patriot missile near the Kuwaiti border.
A major investigation by British and American forces is under way.
The friendly fire - or "blue on blue" - incident happened as the GR4 Tornado returned from a mission over Iraq on Sunday morning.
Wing Commander Mike Oldham, acting Station Commander at RAF Marham in Norfolk, confirmed the deaths.
He said: "They were returning from one of many successful and
professionally conducted missions in Iraq, and I would like
to pay tribute to their expertise and dedication."
Names are not being released before next of kin have been informed.
Wing Cmmdr Oldham added: "Our thoughts and prayers are of course with the families and friends of the
"Here at RAF Marham we live and work as a very close team - today we have lost two valued members of that team."
Group Captain Al Lockwood, chief spokesman for the British forces, said: "This is a tragedy and we are taking rapid steps to find out the reason and to ensure that there is no repetition."
The loss of the jet follows the death of 19 troops - including 14 Britons - in two helicopter crashes in the last few days.
Meanwhile, three members of an ITV news crew remain missing, feared dead after coming under fire in the south of the country. An injured colleague - who escaped - says they came under fire from coalition tanks.
And advancing US forces have suffered four dead and 50 wounded near Nasiriya, while Iraqi television has shown pictures of what it claims to be captured and dead American troops.
The Patriot system is in the Gulf to protect Kuwait and coalition forces from incoming missiles.
UK Defence Secretary Geoff Hoon, who sent his sympathies to the families of the crew, said there were a set of procedures in place to defend British and coalition forces.
"Sadly on this occasion they have not worked and we are conducting urgent reviews, both of the operation of missile batteries as well as of our own aircraft to ensure that this cannot happen again," he told the BBC.
Air Marshal Brian Burridge, commander of British troops in the Gulf, said the accident would not deflect troops from their mission.
He told the BBC: "This is a sad moment but we will put it behind us as quickly as we can in a military sense and carry on to our objective."
RAF Group Captain Jon Fynes said the accident would not harm the coalition, arguing "in many ways it brings us closer together".
"At the base they are sad it happened, but they are now refocused on what needs to be done next."
William Farish, the US ambassador to Britain, paid tribute to the Tornado crew.
He told the BBC: "Friendly fire is something we have lived with for ages throughout wars, but to have it happen in a way like this is very sad."
In a statement Downing Street said the prime minister knew about the accident, adding that he understood it was "an extremely difficult time for those involved, their families and colleagues of the crew who are missing".
Tory leader Iain Duncan Smith said: "I am afraid that it is the nature of warfare and you try to minimise this, but it is a tragedy nonetheless for the families."
The loss of the Tornado came after two Royal Navy Sea King helicopters from the Ark Royal collided over the Gulf on Saturday, with the loss of all seven crew members - six Britons and one American.
A memorial service has been held on board the aircraft carrier for those killed. So far, only one body has been recovered.
On Friday an American CH-46 Sea Knight crashed over the Kuwaiti desert killing eight British and four American service personnel.
The number of accidental deaths amounted to a difficult start to the campaign "and not an ideal one for the UK", Captain Lockwood said.
"It's been tragic and there's been a great deal of sorrow for those concerned and their families and friends."