BAGHDAD (Reuters) - U.S. Secretary of State John Kerry on Wednesday endorsed Iraqi Prime Minister Haider al-Abadi's plans to mend Baghdad's relations with Sunnis and Kurds, and said Iraq was a partner in the fight against Islamic State in Iraq and Syria (ISIS) militants.

Kerry, on a tour of the Middle East to build military, political and financial support to defeat the militants controlling parts of Iraq and Syria, said: "We all have an interest in supporting the new government of Iraq."

"The coalition that is at the heart of our global strategy I assure you will continue to grow and deepen in the days ahead ... because the United States and the world will simply not stand by to watch as ISIL's evil spreads." he said, using an alternative acronym for ISIS.

"A new and inclusive Iraqi government has to be the engine of our global strategy against ISIL. Now the Iraqi parliament has approved a new cabinet with new leaders, with representation from all Iraqi communities, it's full steam ahead."

Kerry's visit comes hours before a speech in which Obama will try to rally Americans behind another war in a region he has long sought to leave, backed by what Washington hopes will be a coalition of NATO and Gulf Arab allies committed to a campaign that could stretch beyond the end of Obama's term in 2016.

"When the world hears from President Obama this evening, he will lay out with great specificity each component of a broad strategy of how to deal with ISIL," Kerry said.

Kerry told Abadi he was encouraged by his plans for"reconstituting" the military and his commitment to political reforms reaching out to all of Iraq's religious and ethnic communities.

Abadi formed his government on Monday in what was billed as a break from the more abrasive style of his predecessor Nuri al-Maliki, whose policies were blamed by many Iraqis for fuelling sectarianism and pushing the country to the brink of collapse.

ISIS fighters seized large chunks of Iraq's north and west this year, welcomed by many of the Sunni Muslim minority, who blamed the government for targeting them with indiscriminate arrests and discriminatory policies.

Abadi appealed to the international community to help Iraq fight Islamic State, urging them "to act immediately to stop the spread of this cancer".

Abadi faces multiple crises, from the need to convince the Sunnis they should stand with Baghdad against Islamic State to persuading minority Kurds not to break away and convincing his own majority Shi'ites he can protect them from Sunni hardliners.

Kerry highlighted Abadi's readiness "to move forward rapidly on the oil agreements necessary for the Kurds, (and) on the representation of Sunnis in government".

In a sign of the eagerness among Iraq's political elite for a fresh start, new Parliament Speaker Selim al-Jubouri, a Sunni, told Kerry: "We are ... hopeful that we will be able to defeat terrorist organisations and establish democracy in Iraq."

Unlike his predecessor, Abadi enjoys the support of nearly all of Iraq's major political groups, and the two most influential outside powers, Iran and the United States. U.S. officials hope he will present a unified front to weaken ISIS, which has seized a third of both Iraq and Syria.

But it will be hard to placate all the forces in Iraq. On Wednesday, cleric Moqtada al-Sadr, head of a powerful Shi'ite movement, said Iraq should not cooperate with "occupiers", a reference to the United States. Sadr's opinions hold sway over tens of thousands of militants.

Three car bombs exploded on Wednesday in a Shi'ite neighbourhood in eastern Baghdad, killing nine people and wounding 29, a police officer said.

While it is unclear what steps will be taken to strengthen the Iraqi army after its collapse in the face of an Islamic State onslaught in June, the senior U.S. official said tentative plans for a new National Guard unit, announced by Abadi on Monday, were intended to deprive ISIS of safe havens by handing over security to the provinces.

Abadi in parliament on Monday described the proposed National Guards units as a means to absorb the Shi'ite militia groups now taking up the slack for a badly depleted army in fighting ISIS. Iraqi and U.S. officials have said the units would be a mechanism for Sunni Muslims to defend their provinces against ISIS.

Kerry also touted the idea during his visit, saying he expected Abadi to take up the initiative in next week's cabinet meeting.

Baghdad has lost control of the main Sunni provinces and the central government has yet to convince Sunnis it can be trusted. Sectarian tensions appeared as entrenched as ever, possibly worsened by a month of U.S. air strikes on Sunni jihadists.

While Kurdish and Shi'ite fighters have regained ground, Sunni Muslims who fled the violence near the northern town of Amerli are being prevented from returning home and some have had their houses pillaged and torched.

Sunni Arabs are also feeling a backlash in villages where they used to live alongside Kurds, who accuse them of collaborating with ISIS.

On Wednesday, Shi'ite militia north of Baghdad forced dozens of Sunni families from their homes during an offensive, stealing possessions and burning houses, a Shi'ite policeman and government source said, asking for anonymity to allow them to report on the offensive, which they said they opposed.

While the U.S. official praised weeks of U.S. air strikes as "highly precise" and "strategically effective", Kerry acknowledged much work lay ahead.

"It's going to be a very difficult, long road to get there," he said, noting that any campaign to defeat Islamic State could take one to three years.

Kerry will meet Jordan's King Abdullah later on Wednesday, and travel on Thursday to Saudi Arabia for talks that will include Egypt, Turkey, Jordan and the Gulf Cooperation Council (GCC), which comprises Saudi Arabia, Bahrain, the United Arab Emirates, Kuwait, Oman and Qatar.

Saudi Arabia is unnerved by the rapid advance of ISIS and fears it could radicalise some of its own citizens. Arab League foreign ministers agreed on Sunday to take all necessary measures to confront ISIS.

In Jordan, Kerry is expected to receive requests for extra military aid, including helicopters and border security equipment, along with part of the US$500 million (S$632 million) the Obama administration has proposed to accelerate training of moderate Syrian rebels, a Jordanian official said.

Jordan is considered a top choice to host the training of the rebels due to its close ties with Washington, proximity to Syria and more than 600,000 Syrian refugees. But Jordan fears retaliation from Syria if it is used for overt training.

French President Francois Hollande will travel to Baghdad on Friday ahead of a conference of regional and international powers in Paris on Monday to coordinate efforts to tackle Islamic State.

After a meeting of EU defence ministers in Milan on Wednesday, Italian Defence Minister Roberta Pinotti told reporters: "We have to try to support and sustain the local protagonists who may be able to stop and contain Islamic State (ISIS) in those areas. The Americans have chosen to carry out air strikes. We haven't yet chosen that.

"We do have refuelling aircraft ... We might have valued assets there. We have training capabilities as well, we can provide training services. We can look at what we might be providing," she said, according to an interpreter.

The Dutch government said it was in discussion with the United States about making a contribution to a force to counter ISIS.