BAGHDAD - Iraq hanged two aides to Saddam Hussein before dawn on Monday but government efforts to avoid a repeat of uproar over the ousted leader's rowdy execution were thwarted when his half-brother's head was severed by the noose.

Many of the government's Shi'ite Muslim supporters rejoiced at the death of Barzan Ibrahim al-Tikriti, Saddam's once feared intelligence chief who was accused of sending people to death in a meat grinder. But voices in Iraq's Sunni Arab minority saw the decapitation as a deliberate sectarian act of revenge.

Government spokesmen said the severing of Barzan's head was a rare hangman's blunder. Critics said it may have been partly a result of Barzan's illness with cancer.

Officials showed journalists film of Barzan and former judge Awad Hamed al-Bander standing side by side in orange jumpsuits on the scaffold, appearing pale and trembling with fear as the hangmen placed black hoods over their heads.

As the two trap doors swung open, the force of the rope jerked Barzan's head off. The head fell to the floor next to his body in a pool of blood as Bander's corpse swung above it.

The officials said they had decided not to distribute any part of the film to the public -- unlike footage shown of Saddam standing on the gallows.

The US ambassador to Iraq, Zalmay Khalilzad, told reporters the hanging of the two men was "an Iraqi decision, an Iraqi execution." But some countries in the European Union, to which Iraq is looking for economic aid, expressed disgust. The United Nations had appealed for mercy.

The government film was silent but officials said there was no disturbance in the execution chamber like the taunting that occurred at Saddam's hanging. The chamber was apparently the same one where Saddam was hanged on December 30.

Supporters of Shi'ite cleric and militia leader Moqtada al-Sadr shouted his name at Saddam's execution, angering Sunnis when illicit film of the scenes emerged. Although Sunnis are an Iraqi minority, they are the majority in the Arab world and view with concern the influence of Shi'ite, non-Arab Iran in Iraq.

SADDAM'S GRAVE

The image of a dignified Saddam going to his death resonated among many round the region and thousands have flocked to his grave in his home village of Awja, near Tikrit.

Convicted with Saddam on November 5 of crimes against humanity over the killing, torture and imprisonment of hundreds of people from the Shi'ite town of Dujail in the 1980s, Barzan and Bander also had their sentences upheld by appeals judges on December 26.

When Prime Minister Nuri al-Maliki ordered Saddam's execution four days later, the two men did not go to the gallows with him -- according to some Iraqi officials because of a lack of US helicopters to transport them.

Chief prosecutor Jaafar al-Moussawi said Bander muttered the Muslim prayer "There is no god but God" but Barzan, a vocal figure in the dock over the past year, was mute with shock.

One official, Bassam al-Husseini, called the decapitation "an act of God."

Barzan's son-in-law hurled a sectarian insult at the government on Al Jazeera television. "As for ripping off his head, this is the grudge of the Safavids," he said -- a historical term referring to Shi'ite ties to non-Arab Iran.

Poor Shi'ites celebrated in Baghdad's Sadr City slum. Moussa Jabor said: "(Barzan) should have been handed over to the people. Execution is a blessing for him."

In Awja, where Barzan and Bander were buried close to Saddam, provincial governor Abdullah al-Juabra said: "People resent the way that Barzan has been executed."

In Cairo, the Arab Organization for Human Rights called for an international medical investigation. The Moroccan Human Rights Association said the hangings were a "criminal political assassination masterminded by American imperialism."

Some Shi'ites were appalled too. Ali Abbas Ridha, a 27-year-old in the northern city of Mosul, said: "What they've done incites people to sectarianism even more. Whether they were executed or not, what's the use?"

Maliki, with the help of some 20,000 more US troops being deployed by President George W. Bush, is preparing a major crackdown on sectarian killers in Baghdad -- including militias who cite loyalty to Sadr and other fellow Shi'ites.

Senior Shi'ite political sources told Reuters the operation had about six months to stave off collapse and civil war.

The top US commander in Iraq said the first troops had arrived but it would take two to three months to see results.