Saudi Arabia seems to have few viable options for pursuing a more independent and forthright foreign policy, despite its deep unease about the West's tentative rapprochement with Iran.
Upset with the United States, senior Saudis have hinted at a range of possibilities, from building strategic relations with other world powers to pushing a tougher line against Iranian allies in the Arab world and, if world powers fail to foil Tehran's nuclear ambitions, even seeking its own atomic bomb.
But alternative powers are hard even to contemplate for a nation that has been a staunch US ally for decades. Russia is on the opposite side to Riyadh over the Syrian war and China's military clout remains modest compared with the United States'.
Robert Jordan, US ambassador to Riyadh from 2001-03, said there would be limits to any Saudi alliances with other powers.
"There is no country in the world more capable of providing the protection of their oil fields, and their economy, than the US, and the Saudis are aware of that. We're not going to see them jump out of that orbit," he told Reuters.
While Jordan was a senior diplomat in the administration of President George W. Bush, some Saudi analysts also say the kingdom is well aware of what major foreign policy shifts would involve - particularly any pursuit of nuclear weapons.
This could end up casting Saudi Arabia as the international villain, rather than its regional arch-rival Iran, and Riyadh has no appetite for the kind of isolation that has forced Tehran to the negotiating table.
"Saudi Arabia doesn't need to become a second Iran," said a Saudi analyst close to official thinking. "It would be a total reversal of our traditional behaviour, of being a reliable member of the international community that promotes strategic stability and stabilises oil markets."
Diplomatic sources and analysts in the Gulf say the kingdom, while unsettled, will not risk a breach in relations with its main non-Arab ally and will explore, however warily, a purely diplomatic response to the Iranian opening.
Top Saudis are nevertheless furious with Washington. Senior US officials held secret bilateral talks with Iranian counterparts for months to prepare for last month's interim nuclear agreement between six world powers and Tehran, raising Gulf Arab rulers' fears that Washington is willing to go behind their backs to do a deal with Iran.
Saudi leaders were taken unawares by the content of the deal that was struck in the early hours of Nov. 24, despite an earlier promise by US Secretary of State John Kerry to keep them informed of developments, diplomatic sources in the Gulf said.
In Washington, a senior State Department official said Kerry had been in close contact with his counterparts throughout the two rounds of negotiations in Geneva, and had talked to Foreign Minister Prince Saud al-Faisal on Nov. 25.
"The agreement was reached in the middle of the night and Secretary Kerry spoke with the Saudi Foreign Minister soon afterward," said the official, who spoke on condition of anonymity.
The agreement offers Tehran relief from sanctions that are strangling its economy, in return for more oversight of its nuclear programme. Riyadh, along with its Western allies, fears this is aimed at producing weapons, a charge Tehran denies.
Iranian Foreign Minister Mohammed Javad Zarif suggested on Sunday the deal should not be seen as a threat. "This agreement cannot be at the expense of any country in the region," he told reporters in Kuwait. "We look at Saudi Arabia as an important and influential regional country and we are working to strengthen cooperation with it for the benefit of the region."
Diplomatic sources in the Gulf say Riyadh is nervous that the deal will ease pressure on Tehran, allowing it more room to damage Saudi interests elsewhere in the Middle East.
The conservative Sunni Muslim kingdom is at odds with Iran's revolutionary Shi'ite leaders in struggles across the Arab world, including in Lebanon, Iraq, Bahrain and Yemen.
Most of all, Riyadh sees Iran's open support for Syrian President Bashar al-Assad in fighting a rebellion backed by Gulf states as a foreign occupation of Arab lands.
Two Iranian Revolutionary Guard commanders have been killed in Syria this year, and rebels have also said Iranian fighters are on the ground, although it is unclear whether they are there in any great numbers. The Lebanese Shi'ite movement Hezbollah, which is allied to Tehran, has also sent fighters to help Assad's forces, although these are Arabs.
Riyadh has expressed lukewarm support for the nuclear deal, couched alongside caveats that it was a "first step" and that a more comprehensive solution required "good will".
But some prominent Saudis have made bold declarations that Riyadh will develop a tough new foreign policy, defending its interests in keeping with its status as the richest Arab state and birthplace of Islam.
Prince Mohammed bin Nawaf, the Saudi ambassador to London, told The Times newspaper that "all options are available" to Riyadh, including seeking its own atomic weapon, if Iran managed to build the bomb.
But diplomatic sources in the Gulf and analysts close to Saudi thinking say the main problem in turning such rhetoric into action is the lack on an obvious replacement for the U.S. security umbrella in the Gulf, or for the American military's role in advising, arming and assisting the Saudi armed forces.
"There'll be more contact with the Russians and Chinese than in the past. They've gone elsewhere for weapons before and we'll see some more of that, but the overall environment will be America-centric," said Jordan.
A Western adviser to Gulf countries on geopolitical issues said senior Saudis have looked at ways of reducing the kingdom's long-term reliance on the United States.
France is one option, albeit one that remains firmly in the Western camp notwithstanding past differences with NATO allies.
Riyadh has worked closely with Paris in recent months on both Syrian and Iranian issues, and has awarded it big naval contracts. That said, the Saudi armed forces and economy are so closely tied to the United States that any serious attempt to disengage over the longer term would be prohibitively costly and difficult, diplomatic sources in the Gulf say.
Washington remains much closer to Riyadh on every Middle Eastern issue than any other world power at present except France, which has taken a hard line on Iran.
In Syria - the issue over which there is the greatest disagreement between Riyadh and Washington, the kingdom is already arming and training some rebel groups which the United States, wary about arming jihadists, views with caution.
Diplomatic sources in the Gulf say these efforts will continue and may expand, but logistical challenges will hinder any rapid attempt to increase training much beyond the thousand or so rebels now working in Jordan with Saudi special forces.
Riyadh's own fears of an Islamist backlash, reinforced by a bombing campaign inside the country in the last decade, prevent it from arming more militant groups with ties to al Qaeda.
The sources say Saudi Arabia still relies on a lot of support from Western allies for command and control expertise, and would find it very difficult to build its own coalition of Arab allies to join forces in a military campaign.
The kingdom and its five closest regional friends, the other members of the Gulf Cooperation Council, have been unable to agree on a shared missile defence shield after years of discussions, they note.
Prince Mohammed's warnings on the possibility of seeking a nuclear bomb have previously been voiced by other top Saudis, including former intelligence minister Prince Turki al-Faisal.
But on closer inspection this looks less like a serious statement of intent and more like an attempt to nudge world powers into being tougher on Iran by raising the spectre of an atomic arms race in the Middle East, where Israel is already widely presumed to have nuclear weapons.
The analyst close to official thinking suggested that actively seeking nuclear arms would backfire, making Riyadh the proliferator of mass destruction weapons instead of Iran.
Media commentators have speculated the kingdom could obtain an atomic bomb from its nuclear-armed friend Pakistan, or on the arms market. But the analyst said it would never place itself in the position of being an international outcast like Iraq under Saddam Hussein and more recently Tehran.
"Iraq did it. Iran did it. Saudi Arabia would never do this type of behaviour," he said.
Saudi Arabia is in the very early stages of planning an atomic power programme, and has signed up to the nuclear non-proliferation treaty and a more rigorous safeguarding protocol with the International Atomic Energy Agency.
Any attempt to build a bomb in secret would probably take decades due to the kingdom's current lack of any nuclear technology, expertise or materials, analysts believe.
Even if it were to attempt to short cut that process by, for example, buying an off-the-peg atomic weapons system from Pakistan - a transaction itself fraught with difficulties - the obstacles would be formidable.
"There's a lot of infrastructure to put in place, to make the threat credible and deliverable. It's not clear to me that Saudi Arabia would be able to do that in short order at all," said Mark Hibbs, a senior associate at Carnegie Endowment for International Peace and nuclear proliferation expert.
Such an effort would also incur a massive price in diplomatic and economic relations with other countries, notably the United States. The Saudi economy, reliant on oil exports and the import of many goods and services from overseas, appears ill suited to withstand such pressures.