Amid calls for its 5,200 troops to leave after a US air strike killed top Iranian and Iraqi commanders this month, here is an overview of the US military presence in Iraq.

- 2003: invasion -

The March 2003 US-led invasion is launched after claims that Saddam Hussein's regime is harbouring weapons of mass destruction.

US forces take control of Baghdad the following month.

President George W. Bush announces the end of major combat operations in May.

In October, a US report says no weapons of mass destruction have been found in Iraq.

Saddam is captured in December and hanged three years later.

The broadcast in April 2004 of images of torture and other abuse of Iraqi prisoners at the Abu Ghraib US military prison shocks the world.

Washington transfers power to an interim government in June.

- Insurgency, conflict -

In November 2004, more than 10,000 American and 2,000 Iraqi soldiers attack the city of Fallujah, retaking it from Sunni insurgents who backed the former regime and Islamic extremists.

In February 2006, Al-Qaeda-linked jihadists blow up a Shiite shrine in Samarra, sparking sectarian killings that leave tens of thousands dead and last until 2008.

In January 2007, Bush boosts the number of US troops in Iraq to 165,000.

- 2011: pullout -

In December 2011 US President Barack Obama withdraws the last American soldiers.

They leave behind an elected Iraqi government but a population scarred by ongoing violence.

Around 4,500 US troops had been killed in Iraq since 2003; at least 112,000 Iraqi civilians also lost their lives, some caught up in fighting and others in sectarian violence or attacks.

- 2014: jihadists -

In January 2014, jihadists capture Fallujah and parts of Ramadi city. In June, they seize Mosul and by the end of 2014 hold one-third of Iraq.

The United States intervenes by bombarding positions of the Islamic State (IS) group and deploys troops to train and equip local security forces.

By mid-2015, there are officially 3,500 American troops stationed in Iraq.

With the help of a US-led coalition, Iraqi forces drive IS from all urban centres, declaring in December 2017 the "end of the war".

- US, Iran tensions -

From late October 2019, US interests in Iraq are hit by a series of rocket attacks blamed on paramilitary groups backed by Iran, which has a growing influence in the country.

A barrage of rockets fired at a military base in Kirkuk in December kills an American civilian contractor and wounds several US and Iraqi soldiers.

The US retaliates with air strikes that kill at least 25 fighters from a hardline pro-Iran paramilitary.

An outraged pro-Iran mob lays siege to the US embassy in Baghdad on New Year's Day.

On January 3, President Donald Trump orders strikes that kill top Iranian commander, Qasem Soleimani, while he is in Iraq, as well as a top paramilitary chief.

Furious Iraqi lawmakers demand the expulsion of the 5,200 US troops in Iraq. Washington pauses joint military operations.

On January 16, the New York Times reports that operations had resumed in order to pick up the fight against the IS.