Top US diplomat John Kerry travelled to Saudi Arabia on Sunday hoping to soothe tensions over Washington's refusal to intervene in Syria and its diplomatic overtures to Iran.
Relations with the longtime ally have been strained over US reluctance to strike Syria or provide more aid to rebels there, as well as its tentative detente with Iran following the election of President Hassan Rouhani, a reputed moderate.
Saudi Arabia has also clashed publicly with Washington over its decision to freeze some aid to Egypt's military-installed government, with Riyadh pledging to more than make up for any shortfalls following the overthrow of Islamist president Mohamed Morsi.
The conservative oil-rich kingdom has grown increasingly nervous over the past two years as Arab Spring revolts have toppled onetime allies in Egypt, Tunisia and Yemen and spread turmoil across the region.
In an unprecedented move last month, Saudi turned down a coveted non-permanent seat on the UN Security Council in protest at the world body's failure to end the war in Syria, which has left over 120,000 people dead.
And last week, Saudi intelligence chief Prince Bandar bin Sultan Al-Saud reportedly told diplomats in Riyadh that he would scale back Saudi cooperation with the CIA on training Syrian rebels and work with other allies including Jordan and France.
"Yes, we are not on good terms with America," read the headline of Sunday's editorial in the local Al-Riyadh daily, which is close to the authorities.
"There are currently differences that could intensify but not lead to a break" in relations between the two allies, most notably over Syria, the daily added.
Saudi Arabia, one of the main backers of rebels struggling to overthrow Syrian President Bashar al-Assad, were infuriated by Washington's decision to forego punitive strikes in favour of a deal struck with Russia to dismantle Syria's chemical weapons.
The accord -- struck in the wake of a chemical weapons attack near Damascus that killed hundreds of people -- has already seen inspectors destroy Syria's chemical arms production equipment and envisages the eradication of its entire arsenal by mid-2014.
Saudi Arabia has also expressed little interest in a US- and Russian-backed initiative to convene Syria peace talks in Geneva next month, going to far as to decline a visit by UN-Arab League envoy Lakhdar Brahimi, a source told AFP.
"There is discontent with the US attitude... and the message has reached" Washington, said Saudi analyst Abdel Aziz al-Sagr, who heads the Gulf Research Centre.
Sunni-majority Saudi Arabia has been locked in a regional rivalry with Iran for decades, and fears a Syrian peace deal that would allow the Tehran-allied regime to stay in power, or a breakthrough in talks over Iran's disputed nuclear programme.
A senior State Department official said Kerry's visit is "one more opportunity to engage on a very high level on all of the issues that we work on with Saudi Arabia."
The official said the United States has been discussing with Saudi Arabia "what is the best way to ensure support for the Syrian opposition coalition, and the military wing of the Syrian coalition, in order to ensure their self-confidence in going to Geneva."
A European diplomat in the Gulf said Saudi Arabia is working with France to arm moderate Islamist rebels, hoping they can make advances on the ground ahead of any talks.
Saudi Arabia is also concerned that Iran could attend the Geneva conference.
Sagr said Riyadh could push for a compromise in which the Organisation of Islamic Cooperation -- a pan-Islamic body based in the kingdom that counts Iran as a member -- participates instead.
The United States has meanwhile sought to assuage Saudi fears -- shared by Israel -- that revived talks could allow Tehran to preserve much of its disputed nuclear programme while seeing the lifting of crippling sanctions.
A new round of negotiations between Iran and the so-called P5+1 group of world powers will be held in Geneva on November 7 and 8, and top administration officials are trying to persuade the Senate to hold off on new sanctions.
"The P5+1 talks are geared towards ensuring that Iran cannot ever obtain a nuclear weapon and on that we completely agree with Saudi Arabia," the State Department official said.
"So that's a question of just making sure they understand the details of how firm our position is."