Iraq war in figures Published duration 14 December 2011

image copyright Reuters image caption All US troops will be out of Iraq by the end of 2011

The US is withdrawing the last of its troops from Iraq, the final phase in the eight-year operation which has cost billions of dollars and many thousands of lives.

The onus of ensuring Iraq's security and rebuilding the devastated country now rests with Iraqi leaders.

Almost every figure related to the war is disputed, with none more keenly debated than the total number of Iraqi deaths. This is a summary of some of the key numbers and the arguments surrounding them.

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US troops led the invasion of Iraq in March 2003, in coalition with the UK and other nations.

The numbers of US "boots on the ground" have mostly fluctuated between 100-150,000 apart from the period of the "surge" in 2007.

This was President George W Bush's drive to improve security in the country, especially in the capital Baghdad, by sending in 30,000 extra troops.

Barack Obama made withdrawal from Iraq a key pledge in his presidential election campaign of 2008 and troop numbers have steadily fallen since he took office in January 2009.

On 19 August 2010, the last US combat brigade left the country, leaving behind 50,000 military personnel involved in the transition process.

British forces peaked at 46,000 during the invasion phase and then fell away year on year to 4,100 in May 2009 when the UK formally withdrew from Iraq.

The Royal Navy continued to train the Iraqi Navy until May 2011. The UK's presence in Iraq is now only as part of the Nato Training Mission - Iraq. That includes 44 military personnel, including a contingent at the Iraqi Military Academy.

The US has lost 4,487 service personnel in Iraq since the start of Operation Iraqi Freedom on 19 March 2003, according to the latest figures from the US Department of Defense

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By 31 August 2010, when the last US combat troops left, 4,421 had been killed, of which 3,492 were killed in action. Almost 32,000 had been wounded in action.

Since then, in what was called Operation New Dawn, 66 have died, of which 38 were killed in action. Three hundred and five have been wounded in action since 1 September 2010.

The UK lost 179 servicemen and women, of which 136 were killed in action.

Other coalition countries account for 139 deaths according to the icasualties website

While coalition troop fatalities are reasonably well documented, deaths of Iraqi civilians and combatants are more difficult to track because of a lack of reliable official figures. All counts and estimates of Iraqi deaths are highly disputed.

The organisation Iraq Body Count has been collating civilian deaths using cross-checked media reports and other figures such as morgue records.

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According to IBC there have been between 97,461 and 106,348 civilian deaths up to July 2010.

The most bloody period for civilian deaths was the month of invasion, March 2003, in which IBC says 3,977 ordinary Iraqis lost their lives. A further 3,437 were killed in April of that year.

The group says the difference between its higher and lower total figures is caused by discrepancies in reports about how many deaths resulted from an incident and whether they were civilians or combatants.

Other reports and surveys have resulted in a wide range of estimates of Iraqi deaths. The UN-backed Iraqi Family Health Survey estimated 151,000 violent deaths in the period March 2003 - June 2006.

Meanwhile, The Lancet journal in 2006 published an estimate of 654,965 excess Iraqi deaths related to the war of which 601,027 were caused by violence.

Both this and the Family Health Survey include deaths of Iraqi combatants as well as civilians.

An unknown number of civilian contractors have also been killed in Iraq. Icasualties publishes what it describes as a partial list with the figure of 467.

The financial scale of the war is another area in which figures vary widely.

The respected and non-partisan Congressional Research Service estimates that the US will have spent almost $802bn (£512.8bn) on funding the war by the end of fiscal year 2011, with $747.6bn (£478bn) already appropriated.

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However, Nobel laureate economist Joseph Stiglitz and Harvard's Linda Bilmes put the true cost at $3 trillion (£1.2tn) once additional impacts on the US budget and economy are taken into account.

The UK has funded its part in the conflict from the Treasury Reserve Fund which is extra money on top of the normal Ministry of Defence budget.

Whitehall figures released in June 2010 put the cost of British funding of the Iraq conflict at £9.24bn ($14.32bn), the vast majority of which was for the military but which also included £557m ($861m) in aid.

Sectarian violence in the conflict began to grow from early 2005. But the destruction of an important Shia shrine in February 2006 saw attacks between Sunni and Shia militias increase dramatically. This caused many Iraqi families to abandon their homes and move to other areas within the country or to flee abroad.

The International Organization for Migration, IOM, which monitors numbers of displaced families, estimates that in the four years 2006-2010, as many as 1.6 million Iraqis [pdf] were internally displaced, representing 5.5% of the population.