The death toll is still considerably smaller than the number of Iraqis who have died in the conflict.
"It has been left to journalists and academics to try and estimate the number that have died. Estimates vary from 89,000 on the lowest side to the highest figure that I have heard - which is one million," James Bays, Al Jazeera's correspondent in Baghdad, said.
"When you speak to an Iraqi who has stayed here in this country throughout the last five years, everyone knows someone who has died, and most families have lost a family member."
Since the US military toppled Saddam Hussein, Iraq's president, it has faced a violent anti-occupation campaign and witnessed violence between the country's sectarian communities.
"No casualty is more or less significant than another; each soldier, marine, airman and sailor is equally precious and their loss equally tragic," Rear Admiral Gregory Smith, US military spokesman in Baghdad, said of the losses.
"Being in the military means we are willingly in harm's way to protect others in order to bring hope and a sustainable security to the Iraqi people."
The milestone death toll comes day after Bush defended his decision to invade Iraq, saying the US would remain in Iraq and promising American soldiers that they would emerge victorious.
'Far from over'
Hoda Abdel Hamid, Al Jazeera's Iraq correspondent, said the high death toll showed that the conflict had not been fully contained by the US.
"The Bush administration keeps saying that things are getting better and better. Reaching such a milestone is a reminder that the war is far from over in Iraq," she said.
"We are at a transition period. Despite the fact that the surge is working, despite the fact that the violence has dropped ... things could get much worse underground."
Abdel Hamid said that the "surge" could not work effectively unless it was accompanied by national reconciliation of Iraq's sectarian communities.
Cause of deaths
More than 80 per cent of soldiers killed have died in attacks by al-Qaeda in Iraq, Sunni and Shia fighters, icasualties.org said.
The remainder died in non-combat related incidents.
Around 40 per cent of those killed were struck by roadside bombs, according to the website, making these weapons the main cause of fatalities.
Small-arms fire was the second biggest killer, the website said, with helicopter crashes, ambushes, rocket attacks and suicide bombings also the cause of many deaths.
The deadliest year for the military in Iraq was 2007 when it lost 901 troops, the icasualties.org website figures said.
This figure compares with 486 deaths in 2003, the first year of the conflict, 849 in 2004, 846 in 2005 and 822 in 2006. Since the start of 2008, 96 soldiers have died.
Vietnam has been the deadliest war for the US military, apart from the two world wars, with 58,000 soldiers killed between 1964 and 1973, an average of 26 a day.
On average, just over two US soldiers die each day in Iraq.
American soldiers in Iraq interviewed by news agencies said that while they were sad about the losses, the conflict was justified.
"It's sad that the number is that high. It makes you wonder if there is a different way of approaching things. Nobody likes to hear that number," said senior Airman Preston Reeves, 26, from Birmingham, Alabama.
|For the US army, 2007 was the deadliest year,|
when it lost 901 soldiers in Iraq [AFP]
"Every one of those people signed up voluntarily and it's a shame that that happens, but tragedies do happen in war.
"It's a shame you don't get support from your own country, when all they want you to do is leave Iraq and all these people will have died in vain."
Against the backdrop of the rising US military death toll, both Hillary Clinton and Barack Obama, Democratic candidates for the 2008 presidential nomination, are calling for the withdrawal of troops.
Clinton has said that she may consider pulling troops out of the country after 60 days, should she win the nomination and the presidency.
But John McCain, who is set to become the Republican candidate in the presidential race, has advocated US soldiers remaining in Iraq.
McCain remains a strong supporter of Bush's controversial "surge", which saw 30,000 extra soldiers deployed in an attempt to improve security in Iraq.