BAGHDAD - The murder at a mosque of the head of the Iraqi parliament's biggest Sunni Muslim bloc could frustrate efforts to seek reconciliation among the country's fractious sectarian and ethnic groups after years of conflict.

But could it tip the battle-scarred country back into all-out sectarian war? The government says that is the likely aim of whoever carried out the assassination, but says those plans will not succeed.

WHY HIM?

Harith al-Ubaidi was recently chosen as head of the Accordance Front, a Sunni bloc that has tried to defend the interests of Iraq's once ruling Sunnis against the majority Shi'ite Muslims who became dominant after Saddam Hussein's fall.

It is part of Prime Minister Nuri al-Maliki's ruling, Shi'ite-led coalition, although it has split with the government before rejoining again and has strained relations with Maliki.

Ubaidi was not particularly well-known, and has not had much of a track record. He was chosen as leader when the former Accordance Bloc head, veteran politician Ayad al-Samarai, was elected speaker of parliament.

Viewed as a moderate, he was also a leading human rights defender in parliament.

Ubaidi might have been targeted because of his moderate stance. More likely, he was killed because he was the head of the biggest Sunni bloc and his death could trigger political repercussions.

WHO MIGHT HAVE KILLED HIM?

The government blamed militants intent on reigniting the sectarian bloodshed that raged between Sunnis and Shi'ites for years and in which tens of thousands of Iraqis died.

Maliki warned on Thursday there would be more violence ahead of national elections due in January.

That could mean al Qaeda, or other Sunni Islamist groups, which are still waging an insurgency against the Iraqi government and U.S. troops despite a sharp fall in violence in Iraq over the past year.

Al Qaeda, which views Shi'ite Muslims as heretics, and Sunni hardliners accuse members of the Accordance Front of being traitors because they take part in the political process.

There has also been speculation that Sunnis might end up joining in a grand alliance with Maliki ahead of parliamentary elections next January. That might further anger hardliners.

Could the killers be Shi'ites? Possibly, although suicidal attacks, as Friday's assassination appears to have been, are more often associated with Sunni extremists.

WILL THERE BE FALLOUT?

Efforts to foster greater reconciliation and dialogue between the Shi'ite-led government and Sunnis may suffer as Sunnis retreat behind a veil of suspicion.

At the same time, the government could end up reaching out more to Sunni lawmakers in a gesture of sympathy and to make it clear that it does not condone the assassination in any way.

Sunnis are suspicious of Maliki.

Many suspect he is a sectarian leader intent on defending the interests of Iraq's once downtrodden Shi'ites and not particularly interested in giving the Sunnis, who repressed Shi'ites under Saddam, a share of power.

The government and its critics have been holding meetings recently to patch over their differences.

Those efforts could be hamstrung while the Accordance Front seeks a new leadership and possibly scuppered if there is any indication of Shi'ite involvement in the murder.

(Editing by Jon Boyle)

Iraq