At the same time, with nine months left in his term, the president must again seek to reassure his Sunni allies upset over American overtures to their regional rival, Shiite Iran.

Obama attends the Gulf Cooperation Council summit in the Saudi capital after reporting progress in recent months against the Islamic State group of Sunni extremists who seized large parts of Iraq and Syria.

Saudi Arabia and other Gulf nations belong to the US-led coalition which carries out air strikes against IS.

Around 4,000 American troops are in Iraq as part of that mission which trains and assists local forces fighting the militants.

The research group IHS said on Monday that Islamic State had lost about 22 percent of its territory in the past 15 months.

In a bid to accelerate gains against the jihadists, Defence Secretary Ashton Carter -- in Riyadh with Obama -- announced on Monday that the US will send more troops and Apache attack helicopters to Iraq.

Washington also wants to emphasise the reconstruction of cities taken back from IS. On Wednesday, Carter pleaded for greater Gulf financial and political involvement in Iraq, which is battling an economic crisis as well as the extremists.

Carter made the comments after meeting his GCC counterparts. “I encourage our GCC partners to do more, not only militarily as the Saudis, as the UAE have been doing... but also politically and economically,” Carter said.

Sunni support for “multisectarian governance and reconstruction” in Shiite-majority Iraq will be critical to ensuring the defeat of IS, the Pentagon chief said.

But Gulf leaders are offended by Obama’s perceived reluctance to get involved in the region’s problems, and in particular his tilt towards Iran, their rival which they accuse of widespread regional interference. AFP