The United States has taken the first step in its expanded fight against Islamic State (IS) militants, going to the aid of Iraqi security forces near Baghdad who were being attacked by enemy fighters.
The US Central Command said it conducted two airstrikes on Sunday and yesterday in support of the Iraqi forces near Sinjar and south-west of Baghdad.
The strikes represent the newly broadened mission authorised by President Barack Obama to go on the offensive against the IS group wherever it is.
Previous US airstrikes in Iraq were conducted to protect US interests and personnel, assist Iraqi refugees and secure critical infrastructure. These strikes were in direct support of Iraqi forces fighting the militants.
Central Command said the strikes destroyed six IS vehicles and one of the group's fighting positions that was firing on the Iraqi security forces.
US officials said the Iraqi forces requested assistance when they came under fire from militants.
Meanwhile, senior Obama administration officials said the US would retaliate against Syrian President Bashar Assad's air defences if he were to go after American planes launching airstrikes in his country.
Officials said the US has a good sense of where the Syrian air defences, along with their command and control centres, are located. If Assad were to use those capabilities to threaten US forces, it would put his air defences at risk.
President Obama has authorised US airstrikes inside Syria as part of a broad campaign to root out IS, though no strikes have yet been launched in the country.
Asked about the prospect of striking Assad's regime if his forces were to target Americans, White House spokesman Josh Earnest said there will be "rules of engagement that are related to any military orders the president directs.
"It won't surprise you to know that there are contingencies related to self-defence when it comes to these sorts of rules of engagement."
The mere discussion of launching strikes in Syria has highlighted the complexity of taking US military action inside a country locked in an intractable civil war.
The conflict has created odd alliances, with both the US and the Assad regime now fighting IS.
However, US officials have ruled out direct co-ordination with Assad and insist that a campaign against the IS will not strengthen the Syrian dictator's hold on power.
US politicians raced to authorise an expanded mission to arm and train moderate Syrian rebels before heading back to the campaign trail.
House Republicans prepared legislation backing a central plank of President Obama's strategy against IS.
The Obama administration says the training operation is needed to establish credible, local ground forces to accompany US air strikes against the militants who have conquered large parts of Iraq and Syria, beheaded two American journalists and become a major US terrorism threat in the region and beyond.
The House and Senate are both on a tight schedule, looking to wrap up work on Friday before an almost two-month recess in preparation for November's elections.
The measure does not authorise US combat troops in Iraq or Syria or explicitly ban them, reflecting a congressional divide between hawks seeking tougher action than that proposed by Mr Obama and politicians weary from more than a decade of U.S. wars in Iraq and Afghanistan.
It also compels the Pentagon to present Congress with a plan 15 days before any training begins, according to a House Armed Services Committee aide.
Democrats are reviewing the proposal, which would enable the military to take over what has previously been a limited, covert operation to beef up rebels fighting extremist groups and Assad's army.
The administration has sent more than 1,000 troops to Iraq to provide military assistance and bolster security of US diplomatic facilities and personnel. But Mr Obama opposes any US ground offensive.
Mr Obama's opposition to ground forces explains why US officials are attaching such importance to enhancing the capacities of Syria's more moderate rebels.
They have received little in military assistance from the US over three-and-a-half years of civil war and have been overwhelmed by opponents on both sides.
The US plan is to develop moderate forces in Saudi Arabia before helping them return to the battlefield. It is unclear how long they will need to be battle ready or how the US can ensure their attention remains on fighting extremists and not just the Syrian government.
Many Republicans and Democrats have expressed reservations about the ability to identify moderates in a country awash with rebel formations and shifting alliances.
The IS grew out of the al Qaida movement, but the two are now fighting. In some instances, the moderate Free Syrian Army has teamed up with al Qaida's local franchise, the Nusra Front.