Iraq's Shiite prime minister Haidar al-Abadi has ordered his air force to halt strikes on civilian areas, following attacks by both Iraqi and US jets in large areas of the country held by Islamic State (IS) fighters.

His announcement on Saturday may be aimed at winning Sunni Muslim support for Dr Abadi's new Shiite-led government as it battles the terrorist group which controls one third of Iraqi territory.

It comes as the United States tries to build regional support for deeper military action against IS in Iraq and Syria.

US secretary of state John Kerry has been touring the Middle East to coordinate a response to IS's growing power in eastern Syria and western Iraq.

In Cairo on Saturday, Mr Kerry said Egypt had a critical role to play in countering the group's hardline Sunni Islamist ideology.

Dr Abadi said his order to protect civilians in Iraq had been issued on Thursday, a day after he held talks with Mr Kerry in Baghdad.

Sunni Muslim tribal figures, who the US hopes can be persuaded to turn against the jihadists, have demanded a freeze on military action on civilian areas as one of the conditions for their support of the Shiite-led government.

But residents in two Sunni areas of Iraq said there had been indiscriminate air strikes in the past two days.

"I have ordered the Iraqi air force to halt shelling of civilian areas even in those towns controlled by ISIS," Dr Abadi said on his official Twitter account, using the former name for militant group Islamic State.

Herak, a Sunni opposition grouping which has led anti-government protests and has ties to armed Sunni groups, said they "positively welcomed" Dr Abadi's comments, a rare break in their usually dissenting rhetoric.

The United Nations' representative in Iraq, Nickolay Mladenov, welcomed the comments which were repeated by Dr Abadi at a conference about refugees on Saturday in Baghdad.

Islamic State took the Iraqi cities of Mosul and Tikrit in June and announced an Islamic caliphate in areas it controls. Its fighters have shocked the world with killings of Sunnis, Shiites, Christians, Yazidis and Kurds.

Western governments and Islamic countries fear their citizens who fight for IS could threaten national security if they return.

Egypt backs need for global action to fight IS

US president Barack Obama plans to strike both sides of the Syrian-Iraqi frontier to defeat IS fighters and build an international coalition for a potentially complex military campaign in the heart of the Middle East.

Egyptian security officials, in particular, are concerned that Egyptian militants based across the border in chaotic post-Gaddafi Libya, who are inspired by IS are plotting against the Cairo government.

Egypt's foreign minister Sameh Shukri said on Saturday during a press conference with Mr Kerry that ties existed between IS and other militants in the region and global action was needed to counter the threat.

"Ultimately this extremist ideology is shared by all terrorist groups," Mr Shukri said.

"We detect ties of cooperation between them and see a danger as it crosses borders."

Egypt's call for international action could bolster Mr Kerry's bid to gather regional support for action in Syria and Iraq.

But Iraq's powerful neighbour Iran - which Mr Kerry said will not join talks in Paris on Monday about confronting IS - accused the US of trying to monopolise the international campaign and blamed Washington for fostering an environment which had allowed the group to flourish.

"In taking a big jump ahead of international bodies, America seeks to emerge as a Hollywood-style hero battling a crisis of its own making," secretary of Iran's Supreme National Security Council, Admiral Ali Shamkhani was quoted as saying.

"America's actions (in coalition-building) are aimed at distracting world public opinion from the central role it played in arming and training terrorist groups to topple the legal Syrian government," he said, according to state news agency IRNA.

'Piecemeal' Third World War has begun, Pope says

A Reuters/Ipsos poll shows 64 per cent of Americans backed Mr Obama's campaign, according to an online survey on Friday. Twenty-one per cent were opposed and 16 per cent said they did not know.

Pope Francis said on Saturday the conflicts in Iraq, Syria and elsewhere were effectively a "piecemeal" Third World War, condemning the arms trade and "plotters of terrorism" for sowing death and destruction.

In the past few months, Francis has appealed for an end to conflicts in Ukraine, Iraq, Syria, Gaza and parts of Africa.

"Humanity needs to weep and this is the time to weep," he said during a visit to Italy's largest war memorial in Redipuglia, Italy, a Fascist-era monument where more than 100,000 soldiers who died in World War I are buried.

Reuters