WASHINGTON (AFP) - US President Barack Obama hailed America's "extraordinary friendship" with Saudi Arabia Wednesday, as he hosted sceptical Gulf leaders for a summit beset by disagreements and royal no-shows.
Describing "an extraordinary friendship and relationship that dates back to Franklin Roosevelt and King Faisal," in the 1940s, Obama heaped praise on two powerful Saudi princes in the Oval Office.
"We are continuing to build that relationship during a very challenging time," Obama said, a nod to conflagrations in Yemen, Syria and Iraq that have reverberated across the Middle East.
Obama praised guests Crown Prince Mohammed bin Nayef and Deputy Crown Prince Mohammed bin Salman, for their work on counterterrorism, which the US President described as "absolutely critical" to the United States.
But conspicuous in his absence at the White House was Saudi leader King Salman, who refused to attend, in what was widely seen as a diplomatic snub, despite Riyadh's insistence it was not.
Five other Gulf leaders - but only two heads of state - are expected to arrive at the White House later in the day, before departing for the presidential retreat at Camp David on Thursday.
During the precursor meeting, the Saudi Crown Prince - well known in Washington as the architect of Saudi Arabia's internal fight against Al-Qaeda - also lauded "the strategic and historic relationship" between the two countries.
But the warm words belied deep malaise over Obama's perceived disengagement from the region and willingness to talk to Iran.
The Arab and largely Sunni Muslim states suspect Obama's nuclear deal with Teheran is a harbinger of a bigger role for their Persian and Shiite arch-foe.
The Gulf states will be seeking assurances from Obama that he is ready to push back against Iranian proxies, in particular in Syria, even if it causes turbulence in sensitive nuclear talks.
They will also want assurances the nuclear deal does not represent a broader "grand bargain" with Iran.
'TILT' TOWARDS TEHERAN?
"What they fear, above all, is that, for one reason or another, American policy is beginning to 'tilt' towards Teheran and away from traditional US allies in the region," said Hussein Ibish of the Arab Gulf States Institute.
Despite close ties stretching back decades, the United States and the conservative Gulf monarchies have never been easy allies.
In 1980, in the wake of crippling oil shock precipitated by Iran's Islamic Revolution, President Jimmy Carter pledged to come to the defence of vital oil-producing Gulf states.
That policy was made manifest a decade later when president George Bush sent troops to Kuwait when it was invaded by Saddam Hussein's Iraq.
Today, the US fifth fleet is based in Bahrain and a US military command center with substantial troops is stationed in Qatar.
But the Gulf states are now asking for the "Carter Doctrine" to be more than a "gentlemen's agreement." With one eye on the US$100 billion-plus windfall that Iran could receive when sanctions end, they would like to see a binding in a mutual defence treaty like that agreed between Nato members.
Such a pact would be difficult to pass through a pro-Israeli Congress, but in any case it is a non-starter for the White House, which relies less and less on Gulf oil, and which sees asymmetric threats and internal unease at closed political systems as a greater security priority.
Since the Arab Spring, President Obama has pointedly warned that closed Gulf monarchical systems must reform if they are to survive.
With reduced attendance and hoped for deals on security and the sale of advanced US weapons like the F-35 stealth fighter in doubt, Obama will have to scramble to salvage the summit.
Officials will likely push for progress on ballistic missile defence, joint military exercises and cyber and maritime security initiatives.