US President Barack Obama has pulled off a diplomatic coup, knitting together a coalition of Arab nations with differing agendas to strike jihadists, but experts question its long-term staying power.

In his speech to the United Nations on Wednesday, Obama warned the battle against extremism would be a multi-faceted "generational task -- and a task for the people of the Middle East themselves."

State Department officials insist the five Arab nations, who joined US fighter jets in an air campaign in the skies above Syria to hit hard against the Islamic State group, are in it for "the long haul."

Washington is well aware of the symbolic importance of having Sunni-ruled Arab states on board to strike against the Sunni extremists, still known to US officials as ISIL.

And Obama met with leaders of Bahrain, Jordan, Saudi Arabia, Qatar and the United Arab Emirates on Tuesday to thank them.

"This is a threat that unifies everybody, and everybody's head around the table was nodding," a senior State Department official revealed.

"Everybody... agreed that there are times in the world when you need to make a stand."

It's the broadest Arab coalition raised by the United States since the 1991 Gulf War, under then president George H.W Bush.

- Just a few bombs -

But experts have cast doubt on just how united it will remain, given the divisions between many Arab nations, and the ever-present spectre of Sunni-Shiite conflict.

"We have a confluence of interests, we have a common enemy, but the question really is are they in it for the long haul? Who knows?" said Kim Holmes, a distinguished fellow at conservative think-tank The Heritage Foundation.

"I mean they didn't have a preponderance of the air power, they dropped a few bombs."

Holmes voiced concerns that normally staunch ally, Britain, as well as Turkey have also yet to join the military action.

"If the going gets tough, and there are for example civilian casualties, or if we're not making sufficient progress, has the president really made a sufficient argument for staying in this fight for what he calls generations, for a long war?" Holmes asked.

Secretary of State John Kerry, who led the painstaking diplomacy to piece together the coalition, said the more partners there are the greater its legitimacy.

"We believe that with the open effort against ISIL from many different players in the region there's going to be much greater confidence," Kerry told CNN.

"There will be more recruits ... morale will go up. People will be more willing to fight."

- Wider conflict -

But Holmes predicted "if ISIL were to be degraded or pushed back significantly I would expect some of the Arabs to start dropping."

Different agendas are also driving Arab cooperation, and could presage a much broader Middle East conflict.

Saudi Arabia wants "control and influence" in the event that regime change arrives in Syria and President Bashar al-Assad is ousted,Ramzy Mardini, an expert at the Atlantic Council, told AFP.

"The Islamic State may only be the rehearsal," he said. "The real show continues to be the power politics in the region and the contest over Syria."

Some observers believe Arab nations are hoping that, in return for their support, the US will help with their own regional and domestic agendas.

"The underlying motive for the Sunni Arab states may be to help the US get through the first-phase of defeating the Islamic State in order to get to the second-phase of changing the regime in Syria," said Mardini.

"This isn't just about targeting militants. It'll likely evolve into something much more consequential for the region."

The Arab world does need to join with the West to fight extremism, argues James Traub in Foreign Policy magazine.

"But the West is not about to join a campaign to crush political opponents on the pretext of fighting terrorism," said the fellow from the Center on International Cooperation.

"Egypt and its new friends in the Gulf will have to do that on their own."