UN High Commissioner for Human Rights Louise Arbour has appealed to Iraq not to execute two top officials from former president Saddam Hussein's rule.
The two men were convicted alongside Saddam Hussein
Ms Arbour said concerns she had about the fairness of Saddam Hussein's trial also applied to his co-defendants.
Her appeal was backed by new UN Secretary General Ban Ki-moon.
It follows speculation that Saddam Hussein's half-brother, Barzan Ibrahim al-Tikriti, and former chief judge Awad al-Bandar are to be hanged soon.
They were sentenced to death over the killings of 148 Shias in the 1980s.
Ms Arbour said she had appealed directly to Iraqi President Jalal Talabani not to carry out the sentences.
She said that under international law the men should have the chance to seek a pardon or have their sentences commuted.
Barzan Ibrahim al-Tikriti - Saddam Hussein's half-brother, former head of the intelligence service
Awad al Bandar - former chief judge of Revolutionary Court
Barzan and Bandar's executions were delayed so that Saddam Hussein could be "executed on a special day", national security adviser Mouwaffaq al-Rubaie said on Saturday.
One government official, Sami al-Askari, denied that a date had been set for the executions.
A spokeswoman for Mr Ban said the UN secretary general was "strongly behind" Ms Arbour's statement.
Ms Arbour made a similar appeal before Saddam Hussein was executed. Her plea comes amid growing controversy over the circumstances surrounding Saddam Hussein's hanging.
On Wednesday, the Iraqi government began an investigation into taunts directed at Saddam Hussein before his execution and the unofficial mobile phone footage shot at the time.
Iraqi officials said at least one guard present at the hanging was being questioned over the unofficial video, which appeared on the internet hours after the execution and showed the moment of death.
The authorities released official footage of Saddam Hussein's execution to prove to the public that he was dead. But that film did not include any sound and did not show the actual moment of death.
Mr Rubaie condemned the appearance of the unofficial footage, calling it an attempt to widen sectarian divides.
A US military spokesman in Iraq, Maj-Gen William Caldwell, said the execution would have been handled differently if the US had been involved.