An American assessment team found "far fewer" Yazidis trapped in northern Iraq than expected, making an evacuation mission less likely, as the flight of minority groups from advancing jihadists showed no let-up Thursday.
The UN refugee agency had said tens of thousands of civilians, many of them from the Yazidi religious minority, were trapped on Mount Sinjar by jihadists of the Islamic State (IS) militant group, which has overrun swathes of Iraq and Syria.
But the Pentagon said that -- based on a firsthand assessment by a small party of US military personnel -- the plight of those on the mountain was not as bad as had been feared, and an evacuation mission was therefore "far less likely".
A US military official said the special forces personnel had returned safely to Arbil, the capital of Iraq's autonomous Kurdish region.
Pentagon press secretary Rear Admiral John Kirby said the fewer than 20 troops did not engage in any combat.
"The team has assessed that there are far fewer Yazidis on Mount Sinjar than previously feared, in part because of the success of humanitarian air drops, air strikes on (IS) targets, the efforts of the (Kurdish forces) and the ability of thousands of Yazidis to evacuate from the mountain each night over the last several days," he said.
"The Yazidis who remain are in better condition than previously believed and continue to have access to the food and water that we have dropped."
Iraqi helicopters and Kurdish forces have been trying to reach those trapped by jihadists who are targeting Yazidis, Christians and other minorities, and Washington and its allies have been studying ways to bring them out.
The Yazidis are a closed Kurdish-speaking community that follows their own non-Muslim faith and are despised by the jihadists as "devil worshippers".
Various countries are ramping up their efforts to aid the trapped civilians and Kurdish forces battling the militants, and the US has launched a series of air strikes since Friday.
But a US military rescue operation on the mountain would take American involvement to another level.
- 'From hunger to hunger' -
Thousands of people have poured across a border bridge into camps in Iraq's Kurdish region after trekking through neighbouring Syria to find refuge, most with nothing but the clothes on their backs.
Some women carried exhausted children, weeping as they reached the relative safety of the camps.
But others, including the most vulnerable, remain trapped on Mount Sinjar, said Mahmud Bakr, 45.
"My father Khalaf is 70 years old -- he cannot make this journey," he told AFP as he crossed back into Iraq.
For those who managed to escape the siege, the relief of reaching relative safety was tempered by the spartan conditions of the camps hurriedly erected by the Iraqi Kurdish authorities to accommodate them.
"We went from hunger in Sinjar to hunger in this camp," said Khodr Hussein.
As the international outcry over the plight of the Yazidis mounted, Western governments pledged to step up help for those still trapped, and the United Nations declared a Level 3 emergency in Iraq, allowing it to speed up its response.
The US said Wednesday it had conducted a seventh airdrop of food and water for those remaining on the mountain, bringing the total aid delivered to the stranded Yazidis in coordination with the Iraqi government to more than 114,000 meals and 35,000 gallons of drinking water.
And Australia has also carried out an aid airdrop, Prime Minister Tony Abbott said Thursday.
Washington has already said it will ship weapons to the Kurds to help them fight back against the jihadists, and France has followed suit.
- Pressure mounts on Maliki -
Washington meanwhile urged Iraqi prime minister designate Haidar al-Abadi to move swiftly to form a broad-based government able to unite Iraqis in the fight against the IS insurgents who have overrun large parts of the country.
Abadi, whose nomination was accepted by President Fuad Masum on Monday, has 30 days to build a team that 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".
The UN Security Council has expressed backing for Abadi's nomination, calling it "an important step toward the formation of an inclusive government."
And the office of top Shiite cleric Grand Ayatollah Ali al-Sistani on Wednesday released a July letter in which he called for incumbent premier Nuri al-Maliki to be replaced.
Maliki has defied growing international pressure to step aside and insisted it would take a federal court ruling for him to quit.
Sistani is revered by millions and has enormous influence among Iraq's Shiite Arab majority.
But even before the release of the Sistani letter, analysts said Maliki had lost too much backing to stay in power.
International support has poured in for Abadi, most importantly from Tehran and Washington, the two main foreign powerbrokers in Iraq.