(Updates toll)

By Mussab Al-Khairalla

BAGHDAD, May 5 (Reuters) - A suicide bomber killed 15 people, mostly police recruits, outside an Iraqi army base west of Baghdad on Saturday in a fresh attack on volunteers for the U.S.-trained local security forces.

Police and an army source said the bomber detonated his explosive-packed vest in a queue of recruits lining up for jobs near Abu Ghraib prison, 30 km (20 miles) west of the capital.

"The bomber got in the line and blew himself up," the army source said. Police said the blast killed 15 and wounded 22. Most of the victims were recruits.

Bombers frequently target Iraqi police and army recruitment centres, which are key to helping build up Iraq's security forces and thus paving the way for the eventual withdrawal of the 150,000 U.S. troops deployed in Iraq.

Last month, a female suicide bomber killed 17 Iraqi police recruits in the town of Muqdadiya, northeast of Baghdad.

A U.S.-backed security crackdown in Baghdad has reduced the number of sectarian killings in the capital, but insurgents have stepped up attacks in the capital's beltways, where U.S. commanders believe militants have regrouped.

U.S. President George W. Bush, who is under pressure from opposition Democrats to set a timetable for withdrawing, has said American forces will leave Iraq when Iraqi troops can take over security in the fight against death squads and insurgents that have pitched the country close to all-out civil war.

POWER STRUGGLE

Shi'ite Prime Minister Nuri al-Maliki says his forces will be ready to control Iraq's 18 provinces by the end of the year.

Under the Baghdad plan, seen as a last throw to secure Iraq, Bush is sending an additional 30,000 troops mostly to the capital and Anbar, the heartland of the Sunni Arab insurgency.

The Abu Ghraib prison sits just outside Baghdad, in Anbar. It gained worldwide notoriety after a prisoner abuse scandal in 2004 involving U.S. troops.

Al Qaeda in Iraq is engaged in a fierce power struggle with local Sunni tribes in Anbar and has stepped up attacks after tribesmen began recruiting locals in a U.S.-backed campaign to expel the Sunni militant group from the province.

Earlier this week, the U.S. military killed Muharib Abdul Latif al-Jubouri, whom it identified as the "senior minister of information" for al Qaeda in Iraq, and two other senior al Qaeda associates in an operation north of Baghdad.

Bush and the U.S. military commander in Iraq, General David Petraeus, have called al Qaeda as "public enemy number one" in Iraq.

On Friday, al Qaeda in Iraq released an audio tape purportedly of its leader, Abu Ayyub al-Masri, who the Iraqi Interior Ministry said was killed in internecine fighting with fellow militants this week.

The authenticity of the tape, posted on a Web site used by Islamists, could not be authenticated and it was not known when it was recorded.

In the 21-minute tape, Masri said reports of infighting were "lies and fabrications" and criticised the Iraqi Islamic Party, the largest Sunni party in parliament headed by Vice President Tareq al-Hashemi, for participating in the Shi'ite-led government. (Additional reporting by Diala Saadeh)

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