Australia's prime minister on Thursday called the deaths of five of the country's soldiers in Afghanistan - three killed by an Afghan army colleague - Australia's worst day in the more than decade-long war.
The Australians were killed in two separate incidents just hours apart late Wednesday and early Thursday.
The first incident took place at a base in Uruzgan province, when a man in an Afghan army uniform opened fire on Australian soldiers, killing three and wounding two, according to Air Marshal Mark Binskin, vice chief of the Australian Defense Force.
Hours later, two Australian soldiers died and a crew member was wounded when their helicopter rolled over while landing in Helmand province.
"In a war of so many losses, this is our single worst day in Afghanistan," Prime Minister Julia Gillard said.
"Indeed, I believe this is the most losses in combat since the days of the Vietnam War and the Battle of Long Tan. This is news so truly shocking that it's going to feel for many Australians like a physical blow."
The Australians were relaxing at the base when the assailant began shooting at close range with an automatic weapon, Binskin said. Soldiers at the base returned fire, but the shooter scaled a fence and escaped.
The Australians tried to revive their comrades, but the wounds proved fatal, he said. One of the wounded soldiers sustained a serious gunshot wound and was evacuated to another base for further treatment. He is in satisfactory condition. The other was treated at the scene.
The Afghan soldier accused of the shooting is named Hekmatullah, and was working as a night guard at the Afghan army base where the international troops had stopped to spend the night, Afghan officials said.
Hekmatullah fired at the Australians as they entered the base in Uruzgan province's Chora district, said Abdulhameed Hameed, an Afghan army commander in the south.
Australian and Afghan soldiers were hunting for the killer Thursday, Binskin said. He would not release further details of the attack, and said the shooter's motive was unknown.
Insider attacks, in which Afghan security forces or insurgents posing as soldiers or police fire on their coalition allies, have been rising over the past year and have surged even higher in the last few weeks. Including the latest strike, there have been at least 34 such attacks so far this year, killing 45 coalition members, mostly Americans. Last year, four Australian soldiers were killed by Afghan troops.
In response to the spike in killings, the U.S. has begun using "guardian angels" - armed NATO service members who are assigned to watch over any gatherings of NATO troops and Afghan soldiers.
Binskin said Australia also uses guardian angels, but he didn't know whether such a soldier was in place during Wednesday's shooting.
Gillard, who in the wake of the deaths will be returning early from a meeting of Pacific nation leaders in the Cook Islands, said security for Australian soldiers had been heightened following the latest attack. She acknowledged the incident was a blow for relations between the two nations' soldiers.
"These insider incidents are very difficult for trust between Australian soldiers and the Afghans that they train. They are corrosive of trust," she said.
Thirty-eight Australian soldiers have been killed in the Afghanistan war, and the latest incidents were the country's worst loss of life in a 24-hour period since the campaign began.
Australia has 1,550 troops in Afghanistan and makes the largest military contribution of any country outside NATO. The Australian soldiers' primary focus is training an Afghan battalion to take responsibility for security in restive Uruzgan.
Australian plans to begin withdrawing troops once the Afghan battalion is fully trained, as early as next year. Gillard said the latest bloodshed would not speed up that timeline.
"Our strategy is well defined, our strategy is constant. And we cannot allow even the most grievous of losses to change our strategy," Gillard said.
"We are there for a purpose and we will see that purpose through."