The Australian government dropped diplomacy on Thursday and called Singapore's plan to hang a young Australian drug smuggler "barbaric".
Australia has repeatedly sought clemency for Tuong Van Nguyen, 25, who was convicted of smuggling 400 grams of heroin from Cambodia through Singapore's Changi airport in 2002.
Attorney-General Philip Ruddock criticised the imposition of the death penalty, especially in Nguyen's case which he said had mitigating circumstances - Nguyen said he smuggled the drugs to try and pay off loan-shark debt for his brother in Australia.
"It was a mandatory death sentence. We feel most remorseful this is going to happen," Ruddock told Australian television.
"It's a most unfortunate, barbaric act that is occurring."
In a tiny concession to Australia, the city-state's prison authority on Thursday allowed Nguyen to hold hands with his mother before his execution but knocked back a request to allow the two a hug one last time.
Then-prime minister Bob Hawke caused a huge rift with Malaysia that lasted a decade when he called the 1986 hanging of two Australian drug smugglers "barbaric".
Singapore is one of Australia's strongest allies in Asia and Australian Prime Minister John Howard has rejected calls for trade and military boycotts over the execution, which is scheduled for Friday at 2200 GMT.
Howard has, however, made five personal pleas to Singapore and his foreign and justice ministers have also called for clemency.
Singapore Prime Minister Lee Hsien Loong on Friday ruled out any last-minute clemency for Nguyen in comments to reporters after meeting German Chancellor Angela Merkel in Berlin.
"The man was charged, convicted, appealed, dismissed. He put up a clemency petition. The petition was considered. All factors were taken into account, including petitions and letters from Australian leaders," Reuters qouted him as saying.