BAGHDAD, Dec 24 (Reuters) - A quarter of Iraq's largest Sunni Arab parliamentary bloc left on Wednesday, weakening the main political voice of the nation's once-dominant minority.

Ten parliamentarians abandoned the Accordance Front bloc over quarrels with fellow members from the Iraqi Islamic Party, said Khalaf al-Ilayan, who heads the Iraqi National Dialogue Council, one of the parties that makes up the bloc.

"Due to the Accordance Front's failure to achieve its mission and the Islamic Party's unilateral actions, we declare ... the Accordance Front has been dissolved," he told a news conference.

But other members of the Front, which would still have about 30 seats in Iraq's 275-member parliament, insisted the Accordance Front was solid.

The split in the Front, formed amid growing sectarianism before 2005 elections, raises doubts about the political unity of Iraq's Sunni Arabs, many of whom are aggrieved more than five years after losing political primacy.

The 2003 toppling of Saddam Hussein, a Sunni Arab who kept his allies close, marked a sea change for Sunni Arabs in Iraq.

The U.S.-led invasion ushered in a new, Shi'ite-led government, while the U.S. decision to purge the government of Saddam's Baath party and disband the military left many Sunni Arabs, and many others, jobless and angry, helping feed an insurgency and sectarian war that left tens of thousands dead.

The splintering comes a day after the resignation of parliament speaker Mahmoud al-Mashhadani, a National Dialogue member whose departure inflamed tensions within the Front.

Violence has dropped sharply in Iraq, and the balance of political power may begin to change next month when Iraq holds provincial elections. Many Sunnis who boycotted past elections are expected to go to the polls and may gain new power.

Hazim al-Nuaimi, a political science professor in Baghdad, said the split reflected growing drift among political allegiances that were formed along sectarian lines.

"It's not just the Accordance Front. It has even happened to the United Iraqi Alliance," he said, referring to the ruling bloc that includes Prime Minister Nuri al-Maliki's Dawa party. (Reporting by Waleed Ibrahim and Aseel Kami; Writing by Missy Ryan)

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