Top US diplomat John Kerry vowed Monday to build an enduring international coalition to defeat the Islamic State, saying almost every nation had a role to play in eliminating the jihadists terrorizing Iraq and Syria.

Speaking only hours before leaving on a mission to solidify the hardening front against the Islamic State (IS), Kerry praised the "new and exclusive" Iraqi cabinet agreed late Monday as a "major milestone" for the war-torn country.

It had "the potential to unite all of Iraq's diverse communities," he said, referring to the sectarian divisions which have plagued the country for years.

With over 40 nations already set to join the US-led coalition to fight the group also known as ISIL, Kerry said "now is the time for Iraq's leaders to govern their nation with the same vision and sense of purpose that helped to bring this new government together."

Kerry will travel first to Amman, in Jordan and then onto Jeddah, Saudi Arabia, but other stops could be likely for the secretary of state, who is known for his whirlwind diplomacy.

President Barack Obama also spoke with new Iraqi Prime Minister Haidar al-Abadi to congratulate him on the formation of a government, even though key security posts remain unfilled.

"The prime minister expressed his commitment to work with all communities in Iraq as well as regional and international partners to strengthen Iraq's capabilities to fight against this common enemy," the White House said in a statement.

Speaking to reporters, Kerry pledged to build "the broadest possible coalition of partners around the globe to confront, degrade and ultimately defeat ISIL."

"Almost every single country has a role to play in eliminating tha ISIL threat and the evil that it represents," Kerry stressed.

Some countries will step up with "military assistance, both direct and in the form of training, arming, advising and equipping."

Others would contribute humanitarian aid for civilians caught in IS's crosshairs, help choke off its funding, and stem the flow of foreign fighters to the battlefields in Iraq and Syria by "demolishing the distortion of one of the world's great peaceful religions" and counter-acting IS propaganda.

- No US boots on ground -

Obama is dispatching Kerry on the eve of a Wednesday speech laying out his "game plan" on how to deal with the Islamic militants, who have beheaded two American journalists, posting shocking on-line videos of their murders.

But Obama has stressed he will not put US boots on the ground, after pulling the last US troops out of Iraq in 2011.

After weeks of US inaction, Obama authorized air operations in early August on IS positions in northern Iraq.

The US military has carried out 148 strikes against the radical Islamic State -- said by US officials to be about 10,000 strong -- who have captured swathes of territory straddling northern Iraq and southern Syria with lightning speed.

Among countries which have publicly declared varying degrees of support are Australia, Canada and Britain, as well as France and the United Arab Emirates.

The 22-member Arab League agreed at a meeting on Sunday in Cairo to take the "necessary measures" to confront the militants.

Countries such as Albania, Estonia, Denmark, Finland and Japan have pledged financial aid for humanitarian assistance to help civilians caught in the battle, according to US officials.

But Kerry has already warned the fight against IS may not be quick, and may even have to be completed by the next White House administration -- which takes over in 2017.

And he vowed the coalition would be built "to endure for the months and perhaps even the years to come."

The coalition building will also continue on the sidelines of the UN General Assembly in New York later in September, when Obama chairs a meeting on stopping foreign fighters from joining the ranks of IS and other militant groups.