KABUL (AFP) - Five Afghan men are due to be hanged on Wednesday for the gang rape of four women after a trial that was severely criticised by rights' groups amid a nationwide outcry over the savage attack.

Then-president Hamid Karzai called for the men to be hanged even before their trial was held last month, and he signed their death sentences shortly before leaving office a week ago.

The armed gang members, wearing police uniforms, stopped a convoy of cars returning to Kabul at night from a wedding in Paghman, a scenic spot near the capital popular with day-trippers.

The attackers tied up men in the group before raping at least four of the women and stealing valuables from their victims.

They were found guilty at a nationally-televised trial that lasted only two hours, and the sentences were quickly confirmed by the appeals court and the Supreme Court.

"The court's verdict on the execution of five men guilty in the Paghman robbery and rape case will be implemented tomorrow," Atta Mohammad Noori, chief of staff at the attorney general's office, told AFP Tuesday.

"It is set to happen, unless there is a last-minute change in the decision."

The August 23 crime has become a symbol of the violence that women face in Afghanistan, despite reforms since the Taleban era.

But the court process raised major concerns over Afghanistan's justice system.

Amnesty International called on President Ashraf Ghani, who was sworn in last week, to stay the death penalties.

"(The trials) have been marred by inconsistencies, un-investigated torture claims and political interference," Amnesty said.

"(Karzai) himself said that he urged the Supreme Court to hand down death sentences. These and similar statements undermined the prospects of a fair trial and the defendants' rights to a presumption of innocence."

Amnesty said the trials had been hurried, giving lawyers little time to prepare the defence. It was only nine days between the arrests and death sentences being handed down by the primary court.

"(Ghani) must ensure that the alleged torture by police of the defendants is independently and thoroughly investigated," the group said.

International donors, including the European Union, have also lodged their objection to the death penalties.

Women's rights have been central to the multi-billion-dollar international development effort in Afghanistan since the fall of the Taleban regime in 2001.

Under the Taleban's harsh version of Sunni Islamic law, women were forced to wear the all-enveloping burqa, banned from jobs, and forbidden even to leave the house without a male chaperone.

The Taleban, who launched a resilient insurgency after being ousted, threaten a comeback as US-led NATO combat troops withdraw from the country at the end of this year.

Ghani's office was not immediately available to comment on the case.