The death toll of US military in Iraq has passed 4,000 after the US Central Command announced that four more troops had died in an attack.

The soldiers were killed on Sunday by a roadside bomb during a patrol in southern Baghdad, the military said on Monday.

At least 50 Iraqis, most of them civilians, also died on Sunday in violence including bomb blasts and shootings.

More than 29,000 American soldiers have been wounded after years of conflict in Iraq, according to the icasualties.org website, which also carried the 4,000-strong US death toll.

Conflict rages

At least 97 per cent of the deaths have come after George Bush, the US president announced the end of "major combat" in Iraq on May 1, 2003.

After the US military toppled Saddam Hussein, Iraq's president, they have faced anti-American campaign and witnessed violence between the country's sectarian communities.

The milestone death toll comes days after Bush defended his decision to invade Iraq, saying the US would remain in Iraq and promising American soldiers that they would emerge "victorious".

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.

'Surge' debate

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.

"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."

Political battle

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, she should 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.

PHOTO CAPTION

A US Army Honor Guard folds the US flag over the casket of an Iraq casualty at Arlington National Cemetery, Virginia, March 10.

Al-Jazeera