BAGHDAD - Iraq's premier designate was gaining widespread support from countries hoping political reconciliation will undercut militants, as Iran Tuesday appeared to further dash Nuri al-Maliki's hopes of clinging to power.

Washington urged Maliki's successor, Haidar al-Abadi, to rapidly form a broad-based government able to unite Iraqis in the fight against militant-led militants who have overrun swathes of the country.

The United States, and other countries, said they were working to deliver much-needed arms to the Kurds, who are fighting the Islamic State (IS) on several fronts.

Abadi came from behind in a protracted and acrimonious race to become Iraq's new premier when President Fuad Masum 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".

"We are urging him to form a new cabinet as swiftly as possible and the US stands ready to support a new and inclusive Iraqi government and particularly its fight against ISIL (IS)," US Secretary of State John Kerry said in Sydney Tuesday.

He also reiterated Washington's stance that US air strikes launched last week were not a prelude to the reintroduction of American combat forces.

In a signal that a key ally of Maliki's was now supporting his rival Abadi, Iran on Tuesday said it backed the legal process which led to him being replaced.

"The framework provided by the Iraqi constitution stipulates that the prime minister has been chosen by the majority group in the parliament," said Ali Shamkhani, secretary and representative of supreme leader Ayatollah Ali Khamenei.

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, militant militants bristling with US-made military equipment they captured from retreating Iraqi troops launched another onslaught this month.

UN rights monitors called Tuesday for the global community to take urgent action to avoid a potential genocide against the Yazidi community in Iraq.

Thousands of members of the Yazidi religious minority are trapped on a mountain in northwestern Iraq with little food or water after Islamic State militants overran the region. "All possible measures must be taken urgently to avoid a mass atrocity and potential genocide within days or hours," said Rita Izsak, the UN's minority rights expert.

They attacked Christian, Yazidi, Turkmen and Shabak minorities west, north and east of Mosul, sparking a mass exodus that took the number of people displaced in Iraq this year soaring past the million mark.

A week of devastating gains saw the militants take the country's largest dam and advance to within striking distance of the autonomous Kurdish region.

Moreover, Britain will send Chinook helicopters to help refugees trapped in northern Iraq, particularly on Mount Sinjar, the government said on Tuesday. ‘As part of our efforts to alleviate humanitarian suffering in Iraq, we are sending a small number of Chinook helicopters to the region for use if we decide we need further humanitarian relief options,’ a spokesman from Prime Minister David Cameron's office said following a meeting of the government's emergency response committee.

Britain has also agreed to transport critical military re-supplies being provided by other contributing nations to the Kurdish forces, so that they could protect refugees in Iraqi Kurdistan from militants of the Islamic State (IS), the spokesman said.

Thousands of people belonging to the Yazidi religious sect have been driven into the arid Sinjar mountain range by Sunni Muslim militants belonging to the IS who want to re-create a mediaeval-style caliphate straddling Iraq and Syria.

The Chinook helicopters, which have a 500-mile operational range, have the capability to land on rough terrain and can be used to deliver heavy loads as well as for evacuations. Britain is already conducting aid drops in the region from C-130 cargo planes and on Tuesday sent Tornado jets to help guide the humanitarian effort. The government said three UK aid drops had already taken place, with two C-130s having delivered 3180 re-usable water containers, filled with a total of 15,900 litres of clean water, and 816 solar lanterns overnight.

Cameron's office has so far dismissed calls from politicians and other commentators to recall parliament from its summer break and debate whether the country should join the United States in intervening militarily against IS.