Three diggers killed in Afghanistan

Three Australian Special Operations troops have been killed and seven more injured when their helicopter crashed in Kandahar in Afghanistan.

Two of the seven injured are in a critical condition, with one in intensive care. All of the men would be transferred to an American base hospital when they stabilise, defence officials said.

One other soldier of unspecified nationality was also killed in the incident.

The helicopter crash was not caused by enemy fire, the Defence Ministry announced.

'A tragic day'

Prime Minister Kevin Rudd paid tribute to the three men moments after news of their death broke.

"This is a tragic day for Australia and the Australian Defence Force," Rudd told parliament.

Rudd expressed sorrow for the friends and families of the three men, and for the injured troops and their loved ones.

He promised that they will receive the best possible medical care.

The three deaths bring Australia's casualty toll in Afghanistan to 16 since it began its engagement there in 2001.

"This is a very heavy price to pay," Rudd said.

"These are exceedingly grim reminders of the dangers our armed forces face, and of the high price that members of our armed forces can be called upon to pay in the service of our country," Opposition Leader Tony Abbott told parliament.

"Our soldiers are men of great character, there is no evidence that any of them are flinching from their duty despite the terrible losses that have been experienced in Afghanistan."

Governor-General Quentin Bryce praised the soldiers' courage, and said it was a heartbreaking day for Australia.

She added that as Australia's Commander-in-Chief she has been struck by the professionalism and comradeship of the

troops she's visited in Afghanistan.

She said the latest victims of the conflict knew its risks and met them with real courage.

Their families should be assured that those who died and are suffering have done so upholding the values that Australians hold dear, she added.

Few details of crash

Defence Chief Air Marshal Angus Houston told reporters he could not specify what kind of helicopter the men were flying in, but said they were on an operational flight.

The craft crashed at 03:39 Afghanistan time. Houston said the men were not reservists, but were on their third tour of duty in the war-torn nation.

The terrain through which the helicopter was flying was "very rugged", according to Houston, and temperatures were high.

The fallen soldiers would be honoured with two seperate ceremonies in Afghanistan before being flown home for another ramp ceremony and their funerals, Houston said.

Fallen sappers honoured

The incident comes just days after two fallen diggers were awarded posthumous medals, following their deaths on a mission in Oruzgan province on June 7.

Sappers Darren Smith and Jacob Moerland and their bomb-sniffing dog were killed by a roadside bomb planted by the Taliban. Their deaths constituted the bloodiest day for Australian troops overseas since the Vietnam war.

Defence Minister John Faulkner told reporters Australia was 'reflecting' on its engagement in Afghanistan, but reiterated that it would remain committed to its operations there.

Australia 'remaining committed'

Australian troops are training the fourth brigade of the Afghan army, and Senator Faulkner said the country would remain committed to that mission.

"We remain very committed to our operational objectives in Afghanistan," he said.

"I think these objectives, these specific goals, these reasons for being in Afghanistan remain of very great importance."

The government's main goal in the central Asian nation is to train Afghan troops.