(Updates with Bush comments, al Qaeda group)

By Fadhil al-Badrani

FALLUJA, Iraq, May 31 (Reuters) - A suicide bomber killed up to 20 men queuing at a police recruitment centre west of Baghdad on Thursday, police said, and al Qaeda militants battled a rival Sunni Arab faction in the south of the capital.

Police and hospital officials said 20 people had been killed and at least 20 more wounded in the Falluja bombing, but the U.S. military said only one policeman had been killed.

The deaths of three more U.S. soldiers were announced on the last day of May, already the deadliest month for U.S. forces in more than two years. A total of 3,473 have died since the U.S.-led invasion in 2003, 122 of them in May.

U.S. President George W. Bush has committed nearly 30,000 additional troops for a major security crackdown aimed at averting all-out sectarian war, but he is coming under growing domestic pressure to bring the soldiers home.

Bush told Iraqi President Jalal Talabani in Washington he was committed to helping the Iraqi government meet important objectives.

"We call them benchmarks, political laws necessary to show the Iraqi citizens that there is a unified government willing to work for the interest of all people," Bush told reporters.

Bush said the laws included oil-revenue sharing legislation and a de-Baathification law and efforts to organise provincial elections.

In Baghdad, the Iraqi government said it was working closely with British authorities to secure the release of five Britons kidnapped from a government building on Tuesday in a raid blamed on the Mehdi Army militia of Shi'ite cleric Moqtada al-Sadr.

Lieutenant-General Raymond Odierno, the deputy U.S. commander in Iraq, said U.S. troops continued to search for the Britons, a computer expert and his four bodyguards.

On Wednesday, soldiers hunting for the hostages used armoured vehicles to smash their way into homes in Sadr City, a Mehdi Army stronghold.

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The Falluja suicide bomber, wearing a vest packed with explosives, walked up to a queue of about 150 young recruits as they waited outside a police station and blew himself up, police spokesman Hamid Abid said.

An Iraqi al Qaeda-led group, the Islamic State in Iraq, said one of its fighters carried out the bombing. It said on a Web site used by insurgents that he used a car bomb.

Bilal Mohammed, a doctor at Falluja hospital, said 20 had been killed and 20 wounded.

Recruitment centres for Iraqi security forces are common targets for such attacks, which are mostly blamed on Sunni Islamist al Qaeda.

Falluja, 50 km (35 miles) west of Baghdad, is in restive Anbar province, a stronghold of the Sunni Arab insurgency.

Some Sunni Arab tribes in Anbar have been encouraging young men to join the Iraqi security forces as part of a new strategy to combat al Qaeda in the area. Al Qaeda in return has responded by attacking those it accuses of cooperating with authorities.

In Ramadi, capital of Anbar, a suicide truck bomber killed five and wounded 15 in an attack on a mobile telephone communications centre.

Anbar remains one of the main battlegrounds for U.S. forces, who have also poured thousands of extra soldiers into Baghdad in an attempt to quell violence between majority Shi'ites and minority Sunni Arabs once dominant under Saddam Hussein.

Al Qaeda is waging a campaign of bombings against Sunni Arab tribes who have formed an alliance against them in Anbar. The Sunni insurgent group the Islamic Army in Iraq also opposes al Qaeda's indiscriminate killings.

On Thursday militants from the two groups turned the streets of Amiriya in southwestern Baghdad into a battleground, residents said. Frightened residents gave varying death tolls. Many fled on foot and merchants shuttered their shops. (Additional reporting by Ross Colvin, Aseel Kami and Mussab Al-Khairalla in Baghdad)

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