Iraq's parliament voted Monday under heavy pressure to approve an inclusive government to win broad support against jihadists, with America's top diplomat due in the region to build an anti-militant coalition.

The outgoing government has faced criticism that by alienating the Sunni Arab minority, it helped create conditions that revitalised Sunni militants including the Islamic State (IS) group, which led a June offensive that seized much of the Sunni heartland.

Washington and the United Nations have repeatedly called on premier-designate Haidar al-Abadi to form a broad-based government.

Giving Sunnis a greater stake in power could help encourage them to join a counter-offensive against the jihadists.

New UN human rights chief Prince Zeid Ra'ad Al Hussein said the atrocities IS had committed in areas under its control had already shown Sunnis that jihadist rule promised only a "house of blood", and the head of Egypt's prestigious Al-Azhar religious institution also condemned the group.

The key parliament session opened with speaker Salim al-Juburi struggling to maintain order among shouting MPs who were sometimes reluctant to remain seated.

There was no official announcement about Abadi's cabinet lineup before the session began, leading one MP to yell at Juburi that they could not vote without knowing the proposed candidates for each specific ministry, and information on their backgrounds.

- Kurds decide to participate -

The issue of Kurdish participation in the government was a major potential sticking point, and their delegation flew from Baghdad to the city of Sulaimaniyah in Iraq's autonomous Kurdish region Monday to discuss the issue with senior political leaders.

US Deputy Secretary of State for Near Eastern Affairs Brett McGurk and UN Iraq envoy Nickolay Mladenov also attended the meeting, an official from the Kurdish Goran Movement said.

When parliament convened, Kurdish MPs had apparently not received final word on whether to take part and were waiting in the cafeteria, but they later arrived in the chamber.

Kurdish MP Ala Talabani announced during the session that the Kurds would participate in the government on a three-month trial period.

In remarks to parliament outlining his proposed programme, Abadi said that "my government is committed to solve all suspended issues with the Kurdistan Regional Government".

The two sides are at odds over various long-running disputes on issues including territory and the division of Iraq's vast oil and gas resources, as well as federal budget payments to the region.

- Obama to announce strategy -

US President Barack Obama, who made his political career opposing the war in Iraq and pulled out American troops in 2011, promised to unveil a long-awaited strategy on Wednesday to tackle IS in both Iraq and neighbouring Syria.

"We are going to systematically degrade their capabilities. We're going to shrink the territory that they control. And ultimately we're going to defeat them," Obama said in an interview aired Sunday on NBC's "Meet the Press".

He said he would not announce the return of US ground troops to Iraq and would focus instead on a "counter-terrorism campaign".

But the difficulties Washington faces were underlined by a report from a Britain-based research group which found that IS fighters were using captured US military-issue weapons supplied to other rebel groups in Syria by Saudi Arabia.

Secretary of State John Kerry was to leave the United States on Tuesday on a trip to Jordan and Saudi Arabia as part of efforts to build an international coalition to counter the IS militants.

A State Department spokeswoman said that more than 40 countries have already indicated a willingness to help out in some way against the jihadists.

- 'House of blood' -

Prince Zeid, the first Muslim and Arab to serve as UN High Commissioner for Human Rights, said that IS had already shown the world what its rule would be like if it was left unchecked.

"It would be a harsh, mean-spirited house of blood," he said in his maiden speech to the UN Human Rights Council. IS "has demonstrated absolute and deliberate disregard for human rights".

The bloodshed continued on Monday when gunmen and suicide bombers attacked the town of Dhuluiyah, north of Baghdad, killing 18 people, police and a doctor said.

Sheikh Ahmed al-Tayyeb, the head of Egypt's Al-Azhar, Sunni Islam's highest seat of learning, also sharply criticised IS jihadists, calling them "criminals" transmitting a "tarnished and alarming image of Muslims".

Arab foreign ministers agreed Sunday to take "necessary measures" against the jihadists, but stopped short of explicitly backing the US air campaign launched in Iraq on August 8.

Washington expanded its air strikes to the Sunni Arab heartland over the weekend, hitting IS targets around a key dam on the Euphrates that troops have been battling to defend with the support of allied tribes.