By Ibon Villelabeitia

BAGHDAD, Jan 3 (Reuters) Facing criticism over an illicit video of Saddam Hussein's hanging, Iraqi officials said today the execution chamber had been infiltrated by outsiders bent on inflaming sectarian tensions.

The video, apparently filmed on a mobile phone and showing Shi'ite officials mocking the former president on the gallows, has caused angry demonstrations among Saddam's fellow Sunni Arabs and sparked international condemnation.

The Shi'ite-led government, embarrassed by images that show a composed-looking Saddam subjected to sectarian taunts as a noose is put around his neck, has set up a committee to investigate who filmed and leaked the video.

''Whoever leaked this video meant to harm national reconciliation and drive a wedge between Shi'ites and Sunnis,'' said National Security Adviser Mowaffaq al-Rubaie, one of a group of 20 officials and other witnesses who were present at the execution at dawn on Saturday.

''There was an infiltration at the execution chamber.'' Echoing those accusations, a senior Interior Ministry official said the hanging was supposed to be carried out by hangmen employed by the Interior Ministry but that ''militias'' had managed to infiltrate the executioners' team.

''The execution was carried out by militias and outsiders.

They put aside the team from the Interior Ministry that was supposed to carry it out,'' the official said.

An official execution video, which had no sound and ended before Saddam falls through the trapdoor, boosted Prime Minister Nuri al-Maliki's authority among his fractious Shi'ite allies.

But the new images have hardened perceptions among Saddam's disillusioned fellow Sunnis of triumphant Shi'ites, dealing a blow to Maliki's efforts for national reconciliation.

U S SAYS IT HAD NO ROLE The U S military, which had kept physical custody of Saddam for three years until he was handed to Iraqis minutes before the execution, said today it had no role in the hanging but that it would have handled it differently.

''Had we been physically in charge at that point we would have done things differently,'' U S military spokesman Major General William Caldwell told a news conference in Baghdad.

Caldwell said U S forces left all security measures at Saddam's execution, including searching witnesses for mobile phones, to Iraqi authorities. He said U S troops immediately left the building where Saddam was executed after handing him over at 5:30 a.m., 25 minutes after he left his U S prison on a 10-minute helicopter ride to the execution site.

''We had absolutely nothing to do with the facility where the execution took place,'' Caldwell said.

Rubaie said he handed over his mobile phone before boarding a U.S. helicopter that transported an official delegation of a little more than a dozen people from the Green Zone government compound to the execution.

Prosecutor Munkith al-Faroon, who also attended the execution and told Reuters he saw two senior government officials film the hanging with their mobiles, said today the taunts came from guards who were outside the chamber.

''These shouts were spontaneous. The guards who called out were outside the chamber,'' he told Al Jazeera.

In the video, however, Saddam is seen reacting to people standing below him. The chanting in support of a Shi'ite cleric and leader of a militia blamed for killing Sunnis appears to come from a voice near the phone.

An adviser to Maliki, Sami al-Askari denied reports that a guard had been arrested over the illicit video.

REUTERS PB HT2155