RIYADH, Saudi Arabia - King Abdullah meets President Barack Obama Friday as mistrust fuelled by differences over Iran and Syria overshadows a decades-long Saudi-US alliance.
Saudi Arabia has strong reservations about attempts by Washington and other major powers to negotiate a deal with Iran on its nuclear programme, and disappointment over Obama's 11th-hour decision last year not to take military action against the Syrian regime over chemical weapons attacks.
Saudi-US relations, dating back seven decades, are "tense due to Washington's stances" on the Middle East, especially Iran, said Saudi analyst Abdel Aziz al-Sagr, who heads the Gulf Research Centre.
The recent rapprochement between Tehran and Washington "must not take place at the expense of relations with Riyadh", Sagr told AFP.
Sunni Muslim Saudi Arabia, long wary of Shiite Iran's regional ambitions, views the November deal with Iran as a risky venture that could embolden Tehran.
The interim agreement curbs Iran's controversial nuclear activities in exchange for limited sanctions relief, and is aimed at buying time to negotiate a comprehensive accord.
Sagr said "arming the Syrian opposition will top the agenda" during Obama's visit, his second since his election in 2009.
Analyst Khaled al-Dakhil spoke of "major differences" with Washington, adding that Obama will focus on easing "Saudi fears on Iran and on regional security".
Saudi Arabia, which leads the six-nation Gulf Cooperation Council, fears that a US withdrawal from the Middle East and a diplomatic overture towards Iran would further feed Tehran's regional ambitions.
Iranian-Saudi rivalry crystallised with the Syrian conflict: Tehran backs President Bashar al-Assad's regime and several GCC states support the rebellion against him.
'Clearing the air'
Obama's stances towards events reshaping the region "have strained (Saudi-US) relations but without causing a complete break," said Anwar Eshki, head of the Jeddah-based Middle East Centre for Strategic and Legal Studies.
US security and energy specialist professor Paul Sullivan said Obama meeting King Abdullah could "help clear the air on some misunderstandings".
"However, I would be quite surprised if there were any major policy changes during this visit. This is also partly a reassurance visit," he added.
White House spokesman Jay Carney has said that "whatever differences we may have do not alter the fact that this is a very important and close partnership".
However, Riyadh seems to be reaching out more towards Asia, including China, in an apparent bid to rebalance its international relations.
Crown Prince Salman bin Abdulaziz this month visited China, Pakistan, Japan and India, to reportedly "strengthen ties".
The US-Saudi relationship dates to the end of World War II and was founded on an agreement for Washington to defend the Gulf state in exchange for oil contracts.
OPEC kingpin Saudi Arabia is the world's top producer and exporter of oil.
Obama and the king are also expected to discuss deadlocked US-brokered Israeli-Palestinian peace talks.
They will also discuss Egypt, another bone of contention since the 2011 uprising which ousted Hosni Mubarak, a staunch US and Saudi ally.
The kingdom was dismayed by the partial freezing of US aid to Egypt, whose army toppled Islamist president Mohamed Morsi in July -- a move hailed by Riyadh.
Egypt's Field Marshal Abdel Fattah al-Sisi resigned as defence minister Thursday after announcing he would stand for president.
Dozens of US lawmakers in a letter to Obama have also urged him to publicly address Saudi Arabia's "systematic human rights violations", including efforts by women activists to challenge its ban on female drivers.