Iraq's parliament was to meet Monday under pressure to approve an inclusive government to win broad support against jihadists, as President Barack Obama prepares to unveil a strategy to defeat them.
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 jihadist group, which led an offensive that seized much of the Sunni heartland in June.
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 fightback against the jihadists.
The 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."
The key parliament session was due to open at 1700 GMT and end with a vote on a new government line-up.
There has still been no word from Abadi's office on the list to be put to MPs and the political horse-trading was expected to go right to the wire.
"I expect changes to occur until the final moments," said Samira al-Mussawi, an MP from Abadi's State of Law alliance.
She said there were persistent "differences over... positions such as deputy prime ministers and some of the key ministries, such as defence and interior."
With Shiite militia playing a key role alongside the regular army in fighting the jihadists, one of their commanders is apparently seeking to turn military gains into political capital, which could complicate efforts to bring Sunnis on board.
Shiite lawmaker Ammar Toma told AFP that outgoing transport minister Hadi al-Ameri, who heads the Badr militia, which has close ties with Iran, was under consideration for the interior portfolio, which would put him in charge of most of Iraq's security forces.
In the previous government, key security ministries were left vacant and run by acting ministers.
Toma said he still expected the political bargaining to be completed in time for the vote to go ahead as planned.
David Petraeus, a former commander-in-chief of US-led forces in Iraq, warned against America becoming an "air force for Shiite militias", which have brutal pasts in the sectarian conflict that gripped Iraq in 2006-8.
Obama, who made his political career opposing the war in Iraq and pulled out US troops in 2011, promised to unveil a long-awaited strategy on Wednesday to tackle IS in both Iraq and neighbouring Syria.
"I'm preparing the country to make sure that we deal with a threat from" IS, 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".
"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.
But the difficulties Washington faces were underlined by a report from a British-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.
The study by Conflict Armament Research found that the jihadists disposed of "significant quantities" of US-made small arms including M-16 assault rifles and included photographs showing the markings "Property of US Govt".
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," Zeid said, stressing that "the scale of its use of brute violence against ethnic and religious groups is unprecedented in recent times."
The bloodshed continued on Monday when militants attacked the town of Dhuluiyah, north of Baghdad, which has held out against their assaults.
Clashes and suicide bombings killed 18 people and wounded more than 50, police and a doctor said.
Arab foreign ministers agreed Sunday to take "necessary measures" against the jihadists but stopped short of explicitly backing the air campaign Washington 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 Valley that troops have been battling to defend with the support of allied tribes.
Iraqi troops and their militia allies sought to capitalise on the strikes, retaking the nearby town of Barwana from the jihadists, an AFP correspondent reported.
However, the victory was marred when a mortar round slammed into the town, wounding provincial Governor Ahmed al-Dulaimi as well as Abdulhakim al-Jughaifi, a local administrative official.