FIVE Australian soldiers have been killed in two separate incidents in Afghanistan, in one of the darkest days of Australia's campaign.
In the first incident, three soldiers were killed in an attack in Oruzgan province by a man wearing an Afghan National Army uniform.
Two other soldiers were also wounded in the incident, Acting Chief of Defence Air Marshal Mark Binskin said.
In the second incident, two Australian Special Forces soldiers were killed when their helicopter crashed in Helmund province.
The three soldiers killed in the first incident were all based at the Gallipoli barracks in Queensland.
One was a 40-year-old lance corporal posted to the 2nd/14th Light Horse Regiment of the Queensland Mounted Infantry.
He was on his second tour of Afghanistan and had previously served in Iraq.
The second soldier was a 23-year-old private posted to 6th Battalion Royal Australian Regiment and the third was a 21-year-old sapper posted to the 2nd Combat Engineer Regiment.
Both were on their first operational deployment.
"Australia has lost five men today, soldiers committed to serving our nation," Acting Chief of Defence Air Marshal Mark Binskin said.
"This is a terrible day for all of us and our thoughts and prayers are with those touched by these incidents."
Air Marshal Binskin said the soldiers were sitting and relaxing after a day's work when a man wearing an Afghan National Army uniform opened fire.
Two other soldiers were injured in the incident and one was evacuated to the Australian base at Tarin Kowt where he is in a satisfactory condition. The other soldier received first aid at the scene and has remained at the base.
Both Australian and Afghan troops are hunting for the Afghan National Army soldier.
"We're currently trying to track him as he's escaped. But I don't want to get into any more details on him at the moment,'' he said.
Air Marshal Binskin said he was not sure of the attacker's motives or the events leading up to the shooting.
The helicopter crash happened at 7.47am (AEST) today, he said.
"It happened on the landing phase and it appears that the helicopter has landed and rolled over, and that's all I know at the moment.''
Prime Minister Julia Gillard has cut short her trip to the Pacific Islands Forum and will fly back to Canberra tonight after the deaths, which she said felt like "a physical blow".
A sombre Prime Minister said Australians would be grieving for the five dead soldiers in what was the worst day of deaths in combat since the Vietnam War.
"This is news so truly shocking that it is going to feel for many Australians like a physical blow," Ms Gillard said.
"If we are feeling that, then it is hard to imagine what the families of these five men are feeling."
"Their loss is immense, their grief will be sharp and our condolences go to each of them as they are confronted by this news."
Ms Gillard said Australians would be justified in questioning why we were still in Afghanistan after the deaths.
But she insisted the mission was working and would come to an end after the draw down of troops over the next 12 to 18 months.
"This is a war with a purpose and a war with an end," she said.
The PM appeared on the verge of tears when she said she had attended too many funerals for soldiers who had died serving Australia.
But she said she had always been struck by the resolve of soldiers' family members to see the war through.
"I understand that this news is bringing immense sadness," Ms Gillard said.
"But even as we will that immense sadness, we must continue to show resolve."
Air Marshal Binskin said morale had "taken a hit'' as a result of the latest incidents.
When it came to so-called "insider threats'' the Taliban would claim any deaths as their own even if the incident was ``a personal grievance or a cultural insensitivity issue''.
But Air Marshal Mark Binskin said Australia remained committed to working with the Afghan forces.
"We're not going to let something like this drive a wedge between us and risk damaging the great progress we've has with the Afghan forces over the last few years.''
But he said both incidents were complex.
Commander-in-Chief of the Australian Defence Force, Governor-General Quentin Bryce, said the loss of five Australian soldiers in the last 24 hours, and the injuries sustained by their mates, signified one of our darkest days.
Ms Bryce expressed her sincere condolences on behalf of all Australians to the families and loved ones devastated by the horrific news.
"I know that Australians everywhere, will pause to think of the families left behind, and the colleagues who will feel this tragic loss deeply''.
"I have spent time with our troops in Afghanistan on three occasions and I am proud of their professionalism, comradeship and strong commitment to duty'', Ms Bryce said.
"They operate in one of the most hostile physical environments on earth, and they understand the enormous risks they face in the line of duty'', Ms Bryce said.
"Their courage is beyond question, and I want to honour and pay tribute to all that our defence men and women do for our country each and every day.''
"These terrible losses will only steel the resolve of those who continue this important work.''
There are 1550 Australian soldiers in Oruzgan province where the troops died.
Before today's developments, Australia had lost 33 soldiers in Afghanistan since 2002.
Another 238 soldiers had been wounded in action, including 25 this year.
So-called “green on blue” attacks - in which Afghan soldiers or police turn on Coalition allies - have become an increasing problem for the International Security Assistance Force.
This is the third incident in which Australian soldiers have been shot and killed by Afghan soldiers in "green on blue" attacks.
In May last year, an Afghan soldier shot and killed Lance Corporal Andrew Jones at a patrol base in the Chorah Valley.
The culprit fled but was subsequently located by US forces and shot dead.
In October last year, another Afghan soldier opened fire on Australian and Afghan troops at a patrol base in Kandahar Province, killing Captain Bryce Duffy, Corporal Ashley Birt and Lance Corporal Luke Gavin.
The Afghan soldier was himself immediately shot dead.
In another incident in November, an Afghan soldier shot and wounded three Australians. He escaped and remains on the run.
In addition to Australians targeted, a number of similar deadly attacks have been launched against British, US and other allied troops.
Earlier, Opposition Leader Tony Abbott said it was a “black day for our military forces”.
“It is a tragic day for the families and comrades of those killed in action,” he said.
News of the deaths came just hours after it was revealed a New Zealand man serving with the Australian Army had lost both of his legs in an explosion last week.
- with Steven Scott and wires