AFP – Blunt talk over the US opening to Iran and reticence in Syria will be on the menu when President Barack Obama travels to Saudi Arabia next month to meet King Abdullah.

Obama’s White House years have caused frustration and incomprehension in Riyadh and a rocky ride for Washington’s key strategic relationship with the Gulf kingdom.

His nuclear diplomacy with Iran, Sunni Saudi Arabia’s Shi’a-led foe in a swirling regional proxy war, and his last gasp reversal on striking Syria last year infuriated the Saudi court.

Since then, Saudi princes, mouthpieces for the aged monarch, have vented in opinion pieces for US newspapers, comparing Washington to a “big bear” reluctant to show its claws and branding an interim nuclear deal with Iran a “dangerous gamble”.

Secretary of State John Kerry, meanwhile, is said to have discovered in recent audiences that the king’s wits and tongue are as sharp as ever, despite his approaching 90th birthday.

Obama’s upcoming visit to Saudi Arabia was first reported Saturday by the Wall Street Journal quoting Arab officials – who appeared to catch Washington off guard.

The White House waited until Monday to confirm that Obama would indeed add an unexpected stop in Saudi Arabia onto a previously announced tour of the Netherlands, Brussels and Vatican City in March.

US officials would not say which partner in the tempestuous marriage of political convenience initiated the summit.

And despite offering “diplo speak” about a broad and vital relationship, they could not quite dispel the idea the visit’s purpose was damage control.

“Whatever differences we may have do not alter the fact that this is a very important and close partnership,” White House spokesman Jay Carney said.

While the picture is not all bleak – Saudi Arabia is cheered by Kerry’s exhaustive Middle East peace drive and the security and intelligence relationship is tight – differences over Iran and Syria are glaring.

“I would expect it to be a very frank conversation, as they say in diplomatic parlance,” said David Ottaway, senior Middle East scholar at the Wilson Center.

Simon Henderson, of the Washington Institute for Near East Policy, said that while the Saudis did not want to humiliate Obama, they would not hide their frustration.

“The undertone is ‘you come here, Mr Obama, we are going to tell you a few facts of life about the Middle East which you don’t appear to appreciate’.”

The Saudis viewed the interim deal world powers clinched with Iran to halt aspects of its nuclear programme in return for some sanctions relief, with undisguised dismay.

The view from Riyadh appears to be that any diplomacy that improves Iran’s position in the region represents a reverse for the kingdom.

“I think it is incredibly difficult for Obama to appease the Saudis,” said Henderson.

Obama’s former defence secretary Robert Gates wrote in his new book that the king told him bluntly that “Iran is the source of all problems and a danger that must be confronted.”

The list of Saudi grievances against the Obama administration begins with disappointment that the president did not do more to live up to his vow for a “new beginning” with the Muslim world delivered in his showpiece speech in Cairo in 2009.

The Saudis fulminated after Obama cast off a long-time US ally in ousted Egyptian president Hosni Mubarak, and threatened by the tide of Arab Spring revolutions, despaired at Obama’s efforts to get on “the right side of history”.

Extraordinary public critiques of Washington by the likes of Prince Turki-al Faisal and Saudi ambassador to Britain, Prince Mohammed bin Nawaf bin Abdulaziz, surfaced after Obama blinked on the brink of unleashing US missiles against President Bashar Al-Assad’s regime in Syria to punish the use of chemical weapons.

The perceived climbdown offered ammunition to Middle East critics who doubt the veracity of Obama’s threat to wage war on Iran if nuclear diplomacy fails.

It also fueled a narrative – which US officials are increasingly trying to dispel – that Washington is disengaging from the Middle East, as Obama brings troops home from foreign battlefields and gazes towards rising Asia.

Saudi frustration that Obama refuses to openly arm anti-Assad rebels spilled over in an emotional intervention by Saudi Foreign Minister Saud al-Faisal during a news conference with Kerry in Riyadh in November.

Syria “is the largest calamity that has befallen the world in the present millennium,” he said in a hushed voice.

“If that isn’t reason enough to intervene, to stop the bloodshed, I don’t know what is.”

While Obama and Abdullah may agree to disagree on Iran and Syria, the US president will highlight Kerry’s Israeli-Palestinian peace effort – which is exactly the kind of US commitment that Saudi Arabia has long demanded.

They also see a common threat from proliferating Al-Qaeda franchises bedding into to restive regions of Syria and Iraq.

Obama last visited Saudi Arabia in the first year of his presidency, in 2009, and welcomed the king to the White House a year later.