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 prime minister 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.

Australian Associated Press