* Sunnis allied with government targeted, officials say
* Al Qaeda behind campaign against moderate Sunnis
* No claim of responsibility
By Suadad al-Salhy
BAGHDAD, Aug 29 (Reuters) - Al Qaeda's Iraq affiliate carried out a suicide attack on a Baghdad mosque that killed more than two dozen people in a campaign against moderate Sunnis allied with the government, Sunni politicians and security officials said on Monday.
The attack on the Umm al-Qura mosque on Sunday recalled the darker days of sectarian violence in 2006-07 when Shi'ite-Sunni fighting pushed Iraq to the edge of civil war.
Leaders of the Iraqi Islamic Party, a major Sunni political bloc, said Islamic State of Iraq (ISI), an affiliate of Sunni Islamist al Qaeda, carried out the bombing to kill one of IIP's most prominent leaders, Sunni lawmaker Khalid al-Fahdawi.
It was part of a campaign against moderate Sunnis that began four weeks ago and has killed seven IIP leaders, they said.
"Al Qaeda has been distributing a lot of leaflets which say that there is no repentance for IIP members anymore, and killing them is allowed everywhere," Rasheed al-Azawi, an IIP leader, told Reuters.
"They want to silence the moderate voices to give the extremists more space inside Sunni areas," Azawi said.
Some Sunni politicians had backed al Qaeda during the last few years but more recently turned against the group as the two sides' interests increasingly conflicted.
Minority Sunnis dominated Iraq under Saddam Hussein but majority Shi'ites took power following the U.S.-led invasion in 2003, leaving some Sunnis feeling politically marginalised.
Security officials say ISI and al Qaeda intend to foment sectarian tensions.
Violence in Iraq has dropped sharply since the height of sectarian bloodletting, but both Sunni Islamists linked to al Qaeda and Shi'ite militias carry out almost daily attacks as U.S. troops prepare to withdraw at the year end.
Militants are increasingly targeting public buildings and security forces in a bid to destabilise the government.
The bomber, wearing a cast on his arm, blew himself up in the main hall of the Umm al-Qura mosque, an important Sunni religious site in the capital's western Ghazaliya district frequented by Sunni leaders.
Ahmed Adbul Ghafour al-Samarrai, the head of the Sunni Endowment, a government-supported body that administers religious sites, said on Monday at a press conference that he was the target of the bomber.
But security officials said initial investigation indicated the bomber could have killed Samarrai and four other prominent Sunni sheikhs but instead blew himself up near Fahdawi and a group of his security guards and followers.
"We think the explosive vest was in the mosque two days before the explosion and the suicide bomber got help from inside," said a senior security source who declined to be named.
"Fahdawi is living in the mosque compound and he was supposed to give a lecture at prayers at that time instead of Samarrai," the source said.
The Iraqi Islamic Party is one of the most prominent Sunni parties. In 2004 it pulled out of the U.S.-backed interim government to protest an American military onslaught on rebel-held Falluja in mostly Sunni Anbar province.
Fahdawi, a relatively quiet voice in parliament, is known as a forceful and stubborn advocate for the Sunni Endowment.
None of Iraq's armed groups claimed responsibility, but suicide bombings are usually employed by Islamic State of Iraq.
Attacks on mosques are especially sensitive in Iraq, where a power-sharing government is struggling to overcome the sectarian slaughter that followed the 2003 U.S.-led invasion.
The Iraqi Health Ministry's statistics department said the mosque blast killed 32 people and wounded another 39.
Security sources put the toll at 18 dead and 22 wounded, while Samarrai said the blast had killed six and wounded 12. Authorities often give conflicting tolls.
Iraqi officials say al Qaeda has resurfaced in former strongholds and is still capable of carrying out large-scale attacks despite losing top leaders and its geographical reach across Iraq.
(Reporting by Suadad al-Salhy; Editing by Elizabeth Fullerton)