Seeking to placate allies 

Seeking to reassure the Gulf allies, White House officials said on Monday the summit would produce announcements on integrating ballistic missile defense systems and increasing joint military exercises.

They said there would also be a statement outlining both US and Gulf states' commitments but were vague about whether that would entail the written US assurances that some Gulf diplomats have sought. The US officials said, however, that they told Gulf states they would not offer a defense treaty, which would face steep obstacles in Congress.

Washington is also poised to offer new weapons under a push for a joint region-wide missile defence system, senior US officials said last week.

"The conspiracy theorists of old have been proven right. The US creates threats for us and then offers us more weapons systems. That does not bode well for us," said Sami Alfaraj, a Kuwaiti security adviser to the six-nation GCC.

Riyadh believes Iranian support for militias in Lebanon, Syria, Iraq and Yemen is the biggest cause of regional instability, aggravating sectarian tensions, undermining strong government and boosting Sunni Muslim jihadists.

The Saudis fear Obama sees a settlement between world powers and Tehran as his legacy. Such a deal on the nuclear program - which the West believes may be aimed at building weapons despite Iranian denials - could lift international sanctions without taming the country's regional ambitions, they think.

Backing from the GCC - made up of Saudi Arabia, Kuwait, Qatar, Bahrain, the United Arab Emirates (UAE) and Oman - is important for Obama to show Congress that the Iran deal has broad regional support, despite Israeli opposition.