US President Barack Obama's trip to Saudi Arabia will likely be met with bitterness by the United States' allies in the Gulf.

Key points: Mr Obama to meet Gulf Cooperation Council summit in Riyadh

Mr Obama to meet Gulf Cooperation Council summit in Riyadh Washington-Gulf relations further strained by Mr Obama's recent Iran comments

Washington-Gulf relations further strained by Mr Obama's recent Iran comments Regional leaders looking ahead to US election in November

On Thursday, Mr Obama will attend the Gulf Cooperation Council summit of leaders from Saudi Arabia, Bahrain, Kuwait, the UAE, Qatar and Oman.

Mr Obama's diplomatic efforts in the region have proved a marked departure from those of his predecessors, and put-out Gulf leaders are looking forward to the United States' November election.

"We don't know why he's coming," said Mustafa Alani, of the Gulf Research Centre, a body funded by a Saudi businessman.

Sunni-led Gulf nations remain deeply offended by Mr Obama rejecting the idea that Saudi foe Iran is the source of all the region's problems.

Mr Obama made the comments last month in an interview with The Atlantic magazine.

Washington–Gulf relations were heavily strained last year when Mr Obama cut a deal with Shiite power Iran to end its economic and diplomatic isolation in return for curbs of its nuclear program.

Mr Obama's senior advisor for the Gulf, Rob Malley, said the United State's relationships in the region are clear.

"I don't think there can be any confusion about who is our partner in the region and who is not," Mr Malley said.

"But if there can be a different relationship between the Gulf Cooperation Council and Iran, it's the President's conviction that is good for the region and good for stability overall."

'Region has changed so much'

Even before coming to office, Mr Obama had dubbed Saudi Arabia a "so-called ally" and had made clear that his diplomatic priorities would be in Asia not the Middle East.

He rubbed salt on those wounds by standing by as Saudi ally Hosni Mubarak was ousted in Egypt, then by his reluctance to back a similar revolt against Syria's Bashar al-Assad.

Lori Plotkin Boghardt, a former CIA analyst at the Washington Institute for Near East Policy, said the Gulf partners would obviously welcome a return to the old relationship.

"But, the region has changed so much, it would be a lot more complicated. Many of them fundamentally want to put Iran back in the box and give it again its pariah status," she said.

The US Congress is considering legislation that would allow the families of victims of the September 11, 2001 attacks to sue the Saudi Government for damages.

No official complicity in the Al Qaeda attacks has been proven, and the White House opposes the draft law, but the Saudi Government is outraged to even see it considered.

AFP