Time was running out for thousands of Iraqis trapped by jihadists, with the US saying on Wednesday it was assessing rescue options and the UN warning of "potential genocide".
The United States has carried out air strikes against members of the Islamic State (IS) jihadist group in the area of Mount Sinjar, where the UN refugee agency says up 20,000-30,000 people, many of them members of the Yazidi minority, are besieged.
Thousands more poured across a bridge into Iraq's autonomous Kurdish region on Wednesday after trekking into Syria to escape, most with nothing but the clothes they wore. Some women carried exhausted children, weeping as they arrived to the relative safety of Iraqi Kurdistan.
But there are still large numbers on the mountain, said 45-year-old Mahmud Bakr. "Many of them are elderly; they cannot walk this distance," Bakr told AFP. "My father Khalaf is 70 years old -- he cannot make this journey. But up there, there is very little food and no medicine," he said.
UN minority rights expert Rita Izsak has warned they face "a mass atrocity and potential genocide within days or hours".
US Secretary of State John Kerry said Wednesday that Washington is looking at options to bring the trapped civilians out. "We will make a very rapid and critical assessment because we understand it is urgent to try to move those people off the mountains," he said.
More US military advisors
Defence Secretary Chuck Hagel said the United States has sent 130 more military advisors to northern Iraq to assess the scope of the humanitarian crisis.
A US defence official said the temporary additional personnel would also develop humanitarian assistance options beyond the current airdrop effort in support of the displaced civilians trapped on Mount Sinjar. The additional personnel are Marines and special operations forces.
Britain said it has agreed to transport military supplies for the Kurdish forces from "other contributing states". And Australian Prime Minister Tony Abbott confirmed Wednesday his country would join humanitarian airdrops in Iraq, and did not rule out the possibility of greater military involvement.
Washington has meanwhile urged Iraqi premier designate Haidar al-Abadi to rapidly form a broad-based government able to unite Iraqis in the fight against jihadist-led insurgents who have overrun swathes of the country.
Abadi came from behind in a protracted and acrimonious process to select Iraq's new premier when President Fuad Masum on Monday accepted his nomination and tasked him with forming a government. He has 30 days to build a team which will face the daunting task of defusing sectarian tensions and, in the words of US President Barack Obama, convincing the Sunni Arab minority that IS "is not the only game in town".
Maliki bid at dead end
Outgoing premier Nuri al-Maliki's hopes of retaining power have been dealt a further blow by Iran, which issued a message congratulating Abadi on his new role.
"We congratulate Haidar al-Abadi on his nomination as prime minister, for him personally and for religious dignitaries, the Iraqi population and its political groups," Ali Shamkhani, secretary and representative of supreme leader Ayatollah Ali Khamenei on Iran's Supreme National Security Council, said in Tehran.
Maliki insists the premiership should be his, declaring Abadi's selection a "constitutional violation", but his bid to retain power has reached a dead end with the widespread international backing for his rival, especially from Tehran and Washington. Maliki on Tuesday ordered the armed forces to "stay away from the political crisis", assuaging fears that he could seek to leverage military power to stay in office.
In an apparent warning to Maliki, US State Department spokeswoman Marie Harf said Tuesday that Washington "would reject any effort, legally or otherwise, to achieve outcomes through coercion or manipulation of the constitutional or judicial process".
"There's a constitutional process, it is happening, and that is what we support."
The political transition comes at a time of crisis for Iraq.
After seizing the main northern city of Mosul in early June and sweeping through much of the Sunni heartland, jihadist militants bristling with US-made military equipment they captured from retreating Iraqi troops launched another onslaught this month. They attacked Christian, Yazidi, Turkmen and Shabak minorities west, north and east of Mosul, sparking a mass exodus that sent the number of people displaced in Iraq this year soaring.
A week of devastating gains saw the IS jihadists take the country's largest dam and advance to within striking distance of the autonomous Kurdish region. US strikes and cross-border Kurdish cooperation have since yielded early results on several fronts, with Kurdish troops beginning to claw back lost ground.