"There are moments of significant agreement and then there are moments of tactical disagreement," US deputy secretary of state Antony Blinken told French radio station Europe 1. "That's the nature of things and I imagine that will continue for the last two years of the Obama administration," added Blinken, who spoke in French.
Prime Minister Benjamin Netanyahu is poised to go to Capitol Hill on Tuesday for another round in an increasingly heated battle with the White House over Iran's nuclear ambitions.
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Obama on Monday lashed out at the Israeli prime minister, pointing to Netanyahu's attacks on a previous interim US-Iran deal that paved the way for this week's ongoing talks in Switzerland.
Blinken stressed that Obama had spent more time in contact with Netanyahu than any other world leader but warned that the Israeli prime minister's speech could have "a bit of a corrosive effect" on ties.
"It does not create trust," said the diplomat, stressing nevertheless that "the U.S. commitment to Israel's security will not change."
Quelling Saudis fears of Iran
Iran and the United States Tuesday returned to the negotiating table for a second day of talks, as a political storm over the issue unfolded thousands of miles away in Washington.
By the shores of Lake Geneva in the town of Montreux, US Secretary of State John Kerry met with his Iranian counterpart Mohammad Javad Zarif as they try to pin down a political framework for a deal to rein in Tehran's nuclear programme by a March 31 deadline. US officials said they began their talks at 9:30 am (8:30 am GMT).
After months of discussions, the two men launched this latest round of talks Monday, and are due to continue negotiating until Wednesday afternoon, when Kerry will fly to Riyadh to meet King Salman to reassure the king that any nuclear deal with Iran is in Saudi Arabia's interest, despite the country's fears it may boost its rival's support for Shi'ite Muslim interests in the region.
Convincing Saudi Arabia to accept any agreed nuclear deal is important to President Barack Obama because he needs Riyadh to work closely with Washington on a host of regional policies and to maintain its role as a moderating influence in oil markets.
The main critics of the US push for a nuclear deal are Israel and congressional Republicans. But Saudi Arabia is skeptical too that any agreement would only let Iran devote more cash and energy to Shi'ite proxies in Syria, Iraq, Lebanon and Yemen, escalating conflicts.
"The Saudis fear Obama will give the Iranians a deal whatever the cost because it is important for his legacy, and that Iran will get a certain regional status in exchange for an agreement," said a diplomat in the Gulf.
Kerry met Iranian Foreign Minister Mohammad Javad Zarif in Montreux, Switzerland, on Monday at the start of up to three days of negotiations to try to meet a self-imposed deadline to achieve a framework agreement by the end of March.
He will then brief Saudi Arabia's new king on the talks, and meet other senior Gulf officials later in the week, in an attempt to convince them that a diplomatic solution to the long-festering crisis over Iran's atomic program is in that country's interest too.
Saudi's anxiety about an agreement has fuelled a flurry of diplomacy in recent days to bolster unity among Sunni states in the Middle East in the face of shared threats including Iran, analysts say.
Washington shares Arab concerns about Iran's role, particularly in Syria and Yemen and through its ties to Lebanon's Hezbollah militia, a senior Obama administration official said, on condition of anonymity, but added that there was a "very substantial" U.S. military commitment to Gulf allies.
"What we need to do is have the appropriate strategies to counter any provocative and destabilizing behavior... it's going to depend on what can we do effectively in places like Syria and Yemen," he said.
US officials are unwilling however to outline what strategies might curb Iran's regional influence, and Washington's record in Iraq, Syria and Yemen - where armed Iranian allies have since flourished - has caused Saudi Arabia great anxiety.
The country's trust in Washington during the Iran talks is also still recovering from the sudden move in late 2013 towards a nuclear deal, when Saudi officials were blindsided by the revelation of months of secret talks between the US and Iran.
"They are very, very nervous about the way we are moving forward," said a Western diplomat who tracks the issue closely and said Riyadh feared a "lose-lose situation" in which Iran either gained an atomic weapon or was freed from sanctions.
Riyadh has long been worried about Iran gaining nuclear weapons capability, something that once led King Abdullah to ask Washington to "cut off the head of the snake" by striking Iran, diplomatic cables released by WikiLeaks showed.
A senior State Department official told Reuters: "Secretary Kerry will make clear we understand the concerns they have about the region's security, concerns that we also share."
AFP and Reuters contributed to this report