Iraqi helicopters dropped supplies Tuesday to thousands of people hiding from jihadists in desolate mountains, many of them from the Yazidi minority which officials warned risked being massacred or starved into extinction.

A Yazidi lawmaker broke down in tears during a parliament session as she urged the government and the international community to save her community from Islamic State militants who overran the Sinjar region.

"Over the past 48 hours, 30,000 families have been besieged in the Sinjar mountains, with no water and no food," said Vian Dakhil.

"Seventy children have already died of thirst and 30 elderly people have also died," she said.

Dakhil said 500 Yazidi men were killed by IS militants since they took over the town of Sinjar and surrounding villages on Sunday. Their women were enslaved as "war booty", she said.

"We are being slaughtered, our entire religion is being wiped off the face of the earth. I am begging you, in the name of humanity."

The United Nations' Children Fund said earlier Tuesday that at least 40 children had died as a result of the IS onslaught on Sinjar, which was previously under the control of Kurdish peshmerga troops.

The town, near the Syrian border, is a hub for Yazidis, a very closed community that follows an ancient faith rooted in Zoroastrianism and referred to by jihadists as "devil worshippers".

Sinjar was also a temporary home for thousands of displaced people from other minorities, such as Shiite Turkmen who had fled the nearby city of Tal Afar when IS launched its offensive on June 9.

The attack on Sinjar sent thousands of people running from their homes in panic, some of them scurrying into the mountains with no supplies.

"Families who fled the area are in immediate need of urgent assistance, including up to 25,000 children who are now stranded in mountains surrounding Sinjar and are in dire need of humanitarian aid, including drinking water and sanitation services," UNICEF said.

-- Hundreds missing --

Iraq's ministry for women's affairs also called for a coordinated Iraqi and foreign intervention to rescue the stranded civilians.

"The ministry appeals to all parties -- the federal government, the Kurdistan government and the international community to urgently put an end to the massacre being carried out by Daash against unarmed civilians," it said, using the Arab acronym for the jihadists.

The Iraqi Red Crescent also insisted decisive action was urgently needed to avert an even greater tragedy.

"Any delay in saving the people of Sinjar will double their suffering, will contribute to increased violence and will encourage Daash to expand its brutal activities," it said.

A Kurdish human rights official told reporters that Iraqi army helicopters had been air-dropping food and water to civilians cowering in the mountains.

Amnesty International also insisted a broader international effort was needed.

"Hundreds of civilians from Sinjar and its environs are missing, feared dead or abducted, while tens of thousands are trapped without basic necessities or vital supplies in the Sinjar Mountain area south of the city," it said.

Pictures posted on the Internet by members of the Yazidi community show little clusters of people gathering on the cave-dotted flanks of a craggy canyon.

Others posted by pro-jihadists purportedly show a jihadist holding the severed head of an alleged Yazidi man from Sinjar.

Yazidis have been chronically persecuted and surviving members fear the latest violence and displacement threatens the very existence of the multi-millennial community on its ancestral land.

"Those people are fighting for their lives in the mountains," said Yazidi rights activist Khodhr Domli. "They are in mortal danger, the entire community is in mortal danger."

Jihadists who already controlled large swathes on the other side of the border with Syria swept into the main northern city of Mosul on June 10 and went on to overrun much of Iraq's Sunni heartland.

The attack on Sinjar and the town of Zumar a day earlier gave IS control over Mosul's hinterland and further abolished the border between the Iraqi and Syrian halves of the "caliphate" the group's leader, Abu Bakr al-Baghdadi proclaimed in June.

The cash-strapped peshmerga have been on the back foot lately but the Kurdish authorities have said a counter-offensive to retake Sinjar and rescue the civilians was under way.