The transfer of two Australians on death row in Indonesia to an island for execution has been delayed to allow them more time with their families, reports said Tuesday.

But as every surviving former prime minister of Australia urged Jakarta to spare Andrew Chan and Myuran Sukumaran from the firing squad, Indonesia's Attorney-General H.M. Prasetyo insisted they would still be killed.

"We are responding to the requests from the Australian government and families," Prasetyo told The Sydney Morning Herald of the postponement.

"We want the families to meet with Myuran and Andrew, to give them more time to be with the convicts on death row. This is not delaying the executions. This is just to provide the families with more time."

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.

They were set to be transported to a high-security prison on the island of Nusakambangan ahead of their execution as early as Wednesday, although no firm date has been announced.

Several other foreigners on death row whose clemency appeals have also been rejected, including from Brazil, France, Ghana, Nigeria and the Philippines, were also expected to be transferred soon.

Prasetyo said he did not know how much more time Chan and Sukumaran would be given, and reiterated that no date had yet been set for the executions.

"This is not something easy. This is not something fun but this is what we must do," he said. "The law states that they have to be executed once clemency has been rejected by the president."

Australia has urged Indonesia -- which faced a diplomatic outcry last month when it executed six drug offenders including five foreigners -- not to proceed, particularly while last-ditch legal measures are being pursued.

Chan and Sukumaran's 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.