SYDNEY (AFP) - The transfer of two Australians to an Indonesian island prison for execution will not go ahead this week as planned, the attorney-general's office said Tuesday, as Canberra pressed for their lives to be spared.

Andrew Chan and Myuran Sukumaran, ringleaders of the so-called Bali Nine heroin trafficking group, were to be transported this week to the high-security prison for their execution, followed by several other prisoners whose appeals for mercy have also been rejected.

Indonesian authorities have confirmed the Australians will be among the next group to face the firing squad, but have remained tight-lipped about which foreign convicts will join them or when the execution will take place.

But attorney-general's spokesman Tony Spontana announced Tuesday the prisoners would not be moved to Nusakambangan Island, off the main island of Java, until a date for their execution had been determined.

"It is delayed. The transfer will not be done this week," he told AFP. "The transfer of the convicts will be carried out closer to the execution date."

Spontana insisted the executions would proceed, but the prisoners would only be taken to the island prison three days beforehand. Death row inmates must be given 72 hours' notice under Indonesian law before facing the firing squad.

The decision to delay the move was made after the Australian government asked for more time for the families to be with their loved ones, Spontana said.

Logistical difficulties involving capacity at Nusakambangan were also cited as a reason.

The Australians and five other foreigners - including citizens from France, Ghana, Brazil and Nigeria - have already lost their appeals for presidential clemency, the final hope of avoiding the firing squad.

Legal and diplomatic efforts to save the Australians have escalated in recent weeks, with every surviving former prime minister of Australia urging Jakarta on Tuesday to spare their lives.

Chan, 31, and Sukumaran, 33, were sentenced to death in 2006 over their roles as ringleaders of a plot to smuggle heroin from Indonesia's Bali island to Australia.

Their lawyers reportedly have a court date next week to look at claims Indonesian President Joko Widodo did not follow the rules in rejecting their clemency bids.

"They cannot transfer, they cannot move Chan and Sukumaran, let alone kill them, while the legal process is going on," Todong Mulya Lubis told the Australian Broadcasting Corporation.

ACT OF MERCY

Widodo has been a vocal supporter of capital punishment and has vowed a tough approach to ending what he has called Indonesia's "drug emergency".

The case of the so-called Bali Nine ringleaders is being followed closely in Australia, a key tourism market for the Indonesian island.

In an unusual show of unity, all of Australia's surviving former prime ministers on Tuesday made a last-ditch plea to spare the men.

"They committed a very serious crime but have demonstrated genuine rehabilitation," said John Howard, whose conservative government began efforts to save the pair during his term in office.

"Mercy being shown in such circumstances would not weaken the deterrent effect of Indonesia's strong anti-drugs laws." From Malcolm Fraser, prime minister from 1975 to 1983, to his successors Bob Hawke, Paul Keating, Howard, Kevin Rudd and Julia Gillard, all the former leaders provided their support for clemency in comments to The Australian newspaper.

"We are very much opposed to the death penalty in Australia," said Fraser while Gillard added: "I personally would find it heartbreaking if such extraordinary efforts to become of good character were not met with an act of mercy, of recognition of change." Rudd, who succeeded Howard as prime minister in 2007, said as a "deep, long-standing friend of Indonesia" he would "respectfully request an act of clemency." Current Prime Minister Tony Abbott has also spoken strongly against the planned executions, warning Canberra will make its displeasure felt if they go ahead.

"Like millions of Australians, I feel sick in the pit of my stomach when I think about what is quite possibly happening to these youngsters," he said Monday.