The four soldiers were killed yesterday in a road bomb attack during a patrol in southern Baghdad, the military said, taking the overall losses of the military in Iraq to 4,000.

Another soldier was wounded in the attack, the military said.

The chaotic and brutal conflict which is now in its sixth year has also left more than 29,000 American soldiers wounded, according to the website.

The bulk of the deaths, at least 97 per cent, occurred after US President George W Bush announced the end of "major combat" in Iraq on May 1, 2003, as the American military became caught between raging anti-American insurgency and brutal sectarian strife unleashed since the toppling of Saddam.

Despite the losses, Bush on the eve of the war's fifth anniversary defended his decision to invade Iraq, vowing no retreat as he promised American soldiers would triumph despite the "high cost in lives and treasure."

According to icasualties.org, 81.3 per cent of the soldiers killed have died in attacks by Al-Qaeda in Iraq fighters, Sunni insurgent groups loyal to Saddam and radical Shiite militias.

The remainder died in non-combat related incidents.