At least 46 people have been killed in a suicide bomb attack targeting Sunni militia west of Baghdad.

The attack happened at around 8.30am local time at an office of the Sahwa in Radwaniyah, a largely Sunni district, 25km from the Iraqi capital.

The US military began recruiting for the Sahwa militia, also known as the Sons of Iraq, among Sunni Arab tribesmen and former insurgents almost four years ago, turning the tide in the war against al-Qaeda in Iraq.

Control of the Sahwa passed to Iraq in October 2008.

Baghdad has promised to incorporate 20% of the Sahwa into the police and military and find civil service jobs for many of the rest, but the process has been slow and is fraught with risks.

In the past six months many Sahwa fighters and members of their families have been killed in revenge attacks.

US begin Iraq in August

The attack comes as US Vice President Joe Biden said the end to his country’s combat missions in Iraq was on schedule for August and would not be delayed if the country failed to form a new government by that deadline.

‘There is a transition government. There is a government in place that's working. Iraqi security is being provided by the Iraqis, with our assistance. We're going to have - still have 50,000 troops there,’ Mr Biden told ABC News' This Week programme in an interview.

Iraq's political parties have been deadlocked since an inconclusive March election over who should form the coalition government and serve as prime minister and president.

‘I don't have a doubt in my mind that we'll be able to meet the commitment of having only 50,000 troops there and it will not in any way affect the physical stability of Iraq,’ Mr Biden said.

US troops intend to end combat operations on 31 August before a full withdrawal by the end of 2011.

Iraqis had hoped the election would lead to stability and economic recovery seven years after the 2003 US-led invasion. But coalition talks could last several more months, exposing Iraq to a risky vacuum as it emerges from sectarian war but struggles to contain a stubborn insurgency.

The sectarian war between once dominant Sunnis and majority Shias that kicked off after the 2003 invasion has largely subsided but a Sunni Islamist insurgency persists.