The hanging of former president Saddam Hussein could not have gone more wrong for the government of Iraqi Prime Minister Nouri al-Maliki.

Instead of ending a dark chapter and making a fresh start, the execution has only managed further to widen the gulf between Iraq's Sunnis and Shias.

The row that has broken out over a mobile phone video of the hanging, in which Saddam is taunted moments before his execution, plus the timing of it just as the Eid al-Adha festival was beginning, threatens finally to bring down the al-Maliki government.

It has already been vainly struggling in its efforts to counter the terrorism wreaking havoc across the country. Now it has its hands further full in dealing with a furious wave of indignation over the execution.

Investigations into how the taunts and the mobile phone video images came about are continuing - but it is long clear that the taunts came from those guarding him, apparently supporters of radical Shia cleric Moqtada al-Sadr.

The Shisd have jubilantly received the images of their former tormentor. But for many Sunnis, the pictures simply proved that what happened was "victor's justice" on a par with lynching.

The most urgent question now is: who took the mobile phone pictures? The government Wednesday said one of the guards had been arrested.

Should he indeed be proved to have taken the pictures, this would be further proof that the Sadr movement - on whose MPs al-Maliki depends for parliamentary support - cannot be relied upon.

But doubts remain. According to deputy chief prosecutor Munqid al-Farun, only two of those present at the execution had mobile phones - national security advisor Muwafak al-Rubaie, and a second government representative. Both were said to have taken pictures.

If it is proved that the pictures originated from one of them, it would be a major blow for al-Maliki, who is already in deep enough trouble as he struggles to stem the tide of violence.

For weeks there have been moves within his Shia alliance to have him replaced, in the hope that someone else at the helm could manage to attract the Sunnis' backing and thus reduce reliance on al-Sadr.

This in turn, so the argument goes, could bring about a "national dialogue" after all, making it a little easier to disarm the al-Sadr militia, one of the strongest within the morass of Iraqi terrorism.

Al-Maliki's main backer, US President George W Bush, has demonstratively expressed his support several times over the past few weeks. But observers are asking how long this can go on.

Al-Maliki recently declared the time was approaching for a government reshuffle.

And in an interview with the Wall Street Journal over the New Year, the 56-year-old was declaring - after just eight months in charge - that he wished he could give up office early.