Iraq's fractious parliament is expected to meet Sunday under heavy pressure to set differences aside and make progress on forming a new government to help counter a raging jihadist-led offensive.

The process could be eased somewhat by agreement among Sunni Arab lawmakers late Saturday on a candidate for speaker of parliament, a role traditionally awarded to the minority group.

"Elections were held in which doctor Salim al-Juburi won the confidence of the lawmakers present, and he was confirmed as the Sunni bloc's candidate for speaker of parliament," a statement from parliament's United for Change Sunni grouping said.

The statement was sent on behalf of a wider meeting of Sunni lawmakers, who also pledged not to accept incumbent premier Nuri al-Maliki for a third term.

Such a condition could be a stumbling block in forming a new government, given Maliki's vow earlier this month to never give up on his candidacy for another turn as Iraqi leader.

World powers and Iraq's top Shiite cleric Grand Ayatollah Ali al-Sistani have appealed to the country's bickering political leaders to unite, but parliament's first session since April polls ended in farce.

MPs had been due to elect a parliamentary speaker on July 1, but instead traded insults and threats, and after a break to cool tempers too few returned to retain a quorum among the 328-member chamber.

"Failing to move forward on electing a new speaker, a new president and a new government risks plunging the country into chaos," UN envoy to Iraq Nickolay Mladenov said in a statement on Saturday.

"It will only serve the interests of those who seek to divide the people of Iraq and destroy their chances for peace and prosperity."

Prospects for a speedy resolution of seemingly intractable differences over key appointments and other issues however appear dim.

Ties between the Baghdad government and Iraq's autonomous Kurdish region have hit new lows in recent days, while Maliki has pledged to seek a third term despite some lawmakers insisting that he step aside.

- Kurd, Arab trouble -

On Friday, the Kurdish region's government claimed disputed northern oilfields, having earlier taken control of other contested areas abandoned by Iraqi forces last month as they fled a sweeping offensive led by jihadists from the Islamic State (IS) group.

Kurdish regional president Massud Barzani has also called for a vote on outright independence, further souring ties with the federal government in Baghdad.

"I think tomorrow's meeting will be the same as the previous one. I doubt the parties will reach agreement on the three nominees," Kurdish lawmaker Rizan Diler Mustafa told AFP on Saturday.

Under an unofficial agreement, the posts of speaker, president and prime minister are allotted to a Sunni Arab, Kurd and Shiite Arab respectively.

Maliki has accused the Kurds of exploiting the insurgent offensive and harbouring militants, while the Kurds say Baghdad is unfairly withholding their share of oil revenues and have called for him to step down.

Maliki, a Shiite Arab viewed by opponents as a divisive and sectarian leader, has no plans to do so, despite eroding political support and thinly veiled calls for change from Washington.

The 64-year-old premier and his coalition partners dominated the April elections, and there is no obvious consensus candidate to replace him.

"We received assurances from the Shiites that Maliki is not going to be prime minister," said Sunni lawmaker Dhafer al-Ani.

In a sign of Washington's concern over the Iraqi crisis, Vice President Joe Biden Saturday spoke by phone with Barzani and also former parliament speaker Osama al-Nujaifi about the need for "all Iraqi political forces" to work to form a new government as soon as possible, the White House said.

It is hoped a new more inclusive government will help drain resentment among Iraq's minority Sunni Arabs, some of whom have aided militant groups.

Iraq's security forces have generally checked the advance, but are struggling to recapture territory, which America's top officer has said is unlikely to happen without outside help.