Iraq conflict: US aid drop follows fresh raids on militants
The US has conducted its second air-drop of food and water to thousands of Iraqis hiding in mountains from jihadist fighters, the Pentagon says.
It came hours after the US launched fresh air strikes against militants from the Islamic State (IS).
The group had recently made fresh gains in northern Iraq and is threatening the Kurdish city of Irbil.
The US is also piling pressure on Iraqi leaders to form a unity government capable of dealing with the jihadists.
A cargo plane carrying British humanitarian aid to Iraq left RAF Brize Norton on Saturday, the BBC understands.
President Barack Obama said on Friday that Iraq's Shia Arab majority had "squandered an opportunity" to share power with the Sunni Arabs and Kurds.
IS, a jihadist group formerly known as Isis, has taken control of swathes of Iraq and Syria and has also seized Iraq's largest dam.
Analysis by BBC Washington correspondent David Willis
President Barack Obama hasn't set a timetable for the current intervention. White House spokesman Josh Earnest said simply that the length of the campaign would be determined by events on the ground.
He said that, ultimately, a solution to the current violence rests with the formation of an Iraqi government that is representative of all the Iraqi people. Yet the course of this engagement is difficult to predict.
White House officials concede they are concerned about the Islamic State fighters' proficiency: they are said to be well armed and well trained, hence it remains to be seen whether air strikes will be effective.
All of which raises the prospect of "mission creep" if the current campaign doesn't halt their advance.
In a statement, the Pentagon said the latest air-drop dispersed 72 bundles of supplies.
The aid was dropped into the mountains around the town of Sinjar, where up to 50,000 members of the Yazidi religious sect fled an IS advance a week ago.
Iraq's human rights ministry believes the militants have seized hundreds of Yazidi women. Ministry spokesman Kamil Amin said some were being held in schools in Iraq's second largest city Mosul.
The first US air strike on Friday saw two 500lb (227kg) bombs dropped on IS artillery being used against forces defending Irbil.
Late on Friday, the Pentagon confirmed a second wave of attacks. It said drones and fighter jets attacked a mortar position and a seven-vehicle convoy carrying fighters also threatening Irbil.
IS remained defiant. One fighter told Reuters that the strikes would have "no impact on us".
"The planes attack positions they think are strategic but this is not how we operate. We are trained for guerrilla street war," he said.
The air strikes are the first time US forces have been directly involved in a military operation in Iraq since American troops withdrew in late 2011.
Marie Harf, a spokeswoman for the US state department, said the immediate goal of the strikes was to "prevent the advance" of IS towards the capital of the semi-autonomous Kurdistan Region, Irbil, where US military personnel and diplomats are based.
UK government sources told the BBC the air strikes were entirely "a US operation" and the UK was currently focused on helping humanitarian efforts.
Although the Iraqi government and the KRG have been at odds for months, Prime Minister Nouri Maliki sent a plane-load of ammunition to Irbil on Friday, Reuters reported.
Ties have been strained by the KRG's decision to send forces into disputed areas of northern Iraq in June after soldiers abandoned their posts in the face of the IS advance; a push by Kurdish leaders for an independence referendum; and Mr Maliki's claim in July that they were giving sanctuary to extremists.
Kurds have also joined Sunni Arabs and some Shia in calling on Mr Maliki to step down because of his handling of the crisis, as well as what they say are the sectarian and authoritarian policies he has pursued.
But as the leader of the bloc that won the most seats in April's parliamentary elections, Mr Maliki has demanded the right to attempt to form a governing coalition.
In an interview with the New York Times, Mr Obama said he was willing to consider broader use of military strikes in Iraq to push back IS and its allies, but warned that Iraq's political leaders had to first figure out how to work with each other.
"We're not going to let them create some caliphate through Syria and Iraq," he said. "But we can only do that if we know that we have got partners on the ground who are capable of filling the void."
The president said that the reason the US had not intervened militarily when IS began its offensive in Iraq in June was "because that would have taken the pressure off of Maliki".
"We're not sending a bunch of US troops back on the ground to keep a lid on things. You're going to have to show us that you are willing and ready to try and maintain a unified Iraqi government that is based on compromise," he added.
- The majority are Chaldeans, part of the Catholic Church
- Numbers have fallen from around 1.5 million since the US-led invasion in 2003 to 350,000-450,000
- In Nineveh province, they live mainly in towns such as Qaraqosh (also known as Baghdida), Bartella, al-Hamdaniya and Tel Kef
- Secretive group whose origins and ethnicity are subject to continuing debate
- Religion incorporates elements of many faiths, including Zoroastrianism
- Many Muslims and other groups view Yazidis as devil worshippers
- There are estimated to be around 500,000 Yazidis worldwide, most living in Iraq's Nineveh plains