Scott Morrison has urged Donald Trump to help ensure a rogue Afghan soldier who killed three Australians remains behind bars.
Hekmatullah, who murdered the officers in 2012, could be released from jail in Afghanistan within days under a prisoner swap brokered by the United States.
The Afghan sergeant was charged over the 2012 deaths of Lance Corporal Stjepan Milosevic, Sapper James Martin and Private Robert Poate in Afghanistan.
The soldiers, all from Queensland, were killed when Hekmatullah opened fire with an automatic weapon.
Two other diggers were wounded in the attack, which occurred inside a patrol base 20km north of Tarin Kowt in Oruzgan province.
The soldier admitted to the shooting and was originally sentenced to death.
Mr Morrison has written to the US president, pleading with him to prevent the killer walking free from Kabul's Pul-e-Charkhi prison.
"Hekmatullah was responsible for murdering three Australians, and our position is that he should never be released," Mr Morrison told reporters in Canberra on Monday.
"We do not believe that his release adds to peace in this region. That is the position that we will continue to maintain and we'll maintain it strongly.
"I can't promise you the outcome we all want here, but it's certainly the outcome that we will continue to press for as hard as we can."
Mr Morrison said Australia had regularly and persistently petitioned for Hekmatullah to remain locked up.
He confirmed the foreign and defence ministers had raised the issue with their US counterparts in Washington DC last month, and he had written to Mr Trump.
"It is a matter of keen interest to Australia, and we've reminded them of that," the prime minister said.
Hekmatullah is one of 400 prisoners who could be released to secure peace with the Taliban.
He has been in prison for just seven years.
The decision to approve the prisoners' release was passed at the end of a three-day "loya jirga" - a traditional Afghan meeting of tribal elders and other stakeholders sometimes held to decide on controversial issues.
"The decision of the loya jirga has removed the last excuse and obstacles on the way to peace talks. We are on the verge of peace talks," said Abdullah Abdullah, who has been appointed by the government to lead negotiations with the Taliban.
"This is a very happy day. Based on the information I have the intra-Afghan talks would begin within two to three days after the release of the 400 Taliban prisoners," former president Hamid Karzai told the gathering.
The gathering recommended that any foreign nationals among the prisoners should be handed over to their respective countries.
The prisoners' fate has been a crucial hurdle in launching peace talks between the two warring sides, which have committed to completing a prisoner exchange before the talks can start.
