Al Qaeda claims responsibility for attack in Iraq

* Al Qaeda group says attack was in highly secure area

* Says army recruits were weapons against Sunnis

BAGHDAD, Aug 20 (Reuters) - Al Qaeda's Iraqi affiliate on Friday claimed responsibility for a suicide attack on an army recruitment centre in Baghdad in which at least 57 recruits and soldiers were killed.

In one of the deadliest incidents of the year, a suicide bomber on Tuesday struck a crowd of young men waiting to hand in job applications to join the Iraqi army.

The attack occurred ahead of the Aug. 31 end to U.S. combat operations in Iraq, a milestone in the war launched by former President George W. Bush 7-1/2 years ago. U.S. troop numbers will fall to 50,000 by the end of the month, from 52,000 now.

In a statement posted on a website often used by Islamist radicals, the Islamic State of Iraq (ISI), a local al Qaeda umbrella group, said the target was in a highly secure area.

"One of the heroes of the State of Islam ... armed with a suicide vest, targeted a gathering of disbelieving cattle and other apostates who sold their religion for little money ...," the statement said.

It said the army recruits were offering themselves as weapons in a war against Sunni Muslims waged by the Shi'ite-led authorities of Iraq.

"Our brother triggered and exploded his vest after plunging himself into the crowd," the statement said.

The sectarian conflict between minority Sunnis and majority Shi'ites that began after the 2003 U.S.-led invasion has largely subsided but a stubborn Sunni Islamist insurgency opposed to Shi'ite dominance of Iraq persists and attacks continue.

The insurgents have sought to exploit a political vacuum created by a failure of Sunni, Shi'ite and Kurdish factions to agree on a coalition government five months after an inconclusive March 7 parliamentary election.

U.S. and Iraqi security officials say the attacks are also a message to supporters that the groups remain effective despite a series of blows to al Qaeda's network, including an April raid that killed Abu Ayyub al-Masri, the leader of al Qaeda in Iraq.

General Ray Odierno, the top U.S. military commander in Iraq, said in early June that 34 of the top 42 al Qaeda leaders in Iraq had been killed or captured in the previous 90 days. (Reporting by Khalid al-Ansary; Editing by Michael Christie)