UN Secretary General Ban Ki-moon deplored the fact that the executions went ahead despite international appeals for clemency.

"He (Ban) regrets that despite pleas from himself and the high commissioner for human rights (Louise Arbour) to spare the lives of the two co-defendants, they were both executed," UN spokeswoman Michele Montas told a press briefing.

On January 6 the new UN secretary general had urged the Iraqi government to to suspend the planned executions.

Saddam's half-brother and former intelligence chief, Barzan Ibrahim al-Tikriti, and the former head of Iraq's Revolutionary Court, Awad Ahmed al-Bandar, were executed early on Monday in Baghdad.

UN human rights chief Arbour sharply criticised the executions, saying they could hamper the long-term search for justice in Iraq.

"I am opposed to capital punishment under all circumstances," she said in a statement.

"In this particular case, not only is the penalty irremediable, it may also make it more difficult to have a complete judicial accounting of other, equally horrendous, crimes committed in Iraq," she added.

The United States, while recognising Iraq's sovereign right to dispense justice as it sees fit, regretted the fashion in which the aides were executed, following Iraq's confirmation that the head of Saddam's half-brother had been ripped from his body during the hanging.

"We were disappointed there was not greater dignity given to the accused under these circumstances," said US Secretary of State Condoleezza Rice.

Britain, the staunchest US-ally over the war in Iraq, restated its opposition to the death penalty but said justice had taken its course.

"Ultimately... this was a decision for the sovereign government," a Foreign Office spokesman in London told AFP.

Prime Minister Tony Blair's official spokesman gave the same line, saying: "Iraq is a sovereign government and therefore has a right under international law to decide its own policy on the death penalty."

Saddam's execution on December 30, before which he was taunted by Shiite guards and observers, drew criticism worldwide for the way it was handled by the Iraqi authorities.

Grisly images of the execution and Saddam's body recorded on a mobile phone and posted on the Internet only served to fuel the sense of outrage.

European Commission president Jose Manuel Barroso and Italian Prime Minister Romano Prodi, both of whom had condemned Saddam's hanging, were equally blunt in denouncing the execution of his aides.

"I have the same position I had over the execution of Saddam Hussein," Prodi said. "Italy is against the death penalty."

Barroso added: "We are in principle against the death penalty. Man does not have the right to take the life of another man."

Capital punishment is outlawed in all European Union countries, but it is widely practiced in two of the UN Security Council's five permanent members -- China and the United States.

Iraq's neighbour Jordan said it hoped that the executions would not undermine the reconciliation process in Iraq.

Human rights group Amnesty International said the hangings only served to underline the brutal and inhuman nature of capital punishment.

"Saddam Hussein and his aides should certainly have been held to account for the horrific human rights crimes committed by his government," said Amnesty official Malcolm Smart.

"But this should have been through a fair trial process and without recourse to the death penalty," which was a "brutal violation of the right to life," Smart said.

And he added: "Reports that Barzan Ibrahim al-Tikriti had his head severed during the hanging only emphasise the brutality of this already cruel, inhuman and degrading punishment."