Afghan president Hamid Karzai is moving to replace the country's intelligence chief and the ministers of defence and interior.
The planned reshuffle is the first step in what senior government officials said was a planned wider cabinet shake-up aimed at solidifying the president's power before elections and the drawdown of foreign forces.
Mr Karzai is also trying to shore up his shaken security team as his administration struggles to build an army and police force in the face of a resurgent Taliban as the US and other foreign forces begin to withdraw.
Meanwhile, three Australian soldiers were killed and two wounded in Afghanistan after a man in an Afghan army uniform opened fire and another two Australian soldiers were killed in an unrelated helicopter crash. The nation's prime minister said the deaths made it Australia's worst day in the ongoing war.
The first three soldiers were killed while relaxing at a base on Wednesday evening, when a man wearing an Afghan National Army uniform opened fire on them with an automatic weapon at close range, Air Marshal Mark Binskin, vice chief of the Australian Defence Force, said.
Australian soldiers at the base in Uruzgan province returned fire, but the shooter scaled a fence and escaped from the base, Mr Binskin said.
The Australians tried to revive their comrades, but the wounds proved fatal. One of the two wounded soldiers sustained a serious gunshot wound and was evacuated to another base for further treatment. He was in satisfactory condition. The second wounded soldier was treated at the scene.
In a second, unrelated incident early today, two Australian soldiers died after their helicopter rolled over while landing in Helmand province. A crew member on board was also wounded.
Prime minister Julia Gillard, in the Cook Islands for a forum of Pacific nation leaders, said she would be returning to Australia early in the wake of the deaths.
"In a war of so many losses, this is our single worst day in Afghanistan," she 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."