Beneath this weekend's rupture in Iranian-Saudi relations lies a deeper fault line between the United States and Saudi Arabia that may hamper U.S. President Barack Obama's efforts to end Syria's civil war, current and former U.S. officials said.

The Saudi government's decision to execute Shia cleric Sheikh Nimr al-Nimr on Saturday, despite U.S. warnings, illustrated the limits of U.S. influence over the kingdom.

And the Saudi decision to cut diplomatic ties to Iran after outraged Iranian protesters entered, and set fire to, the Saudi embassy in Tehran, runs directly counter to U.S. efforts to promote contact between the two nations, particularly on Syria.

U.S. Secretary of State John Kerry's longshot effort to bring the nearly five-year Syria civil war to an end may be the first casualty of the latest tensions.

The Saudi ambassador to the United Nations, Abdallah Al-Mouallimi, on Monday said the Saudis will attend UN-sanctioned talks set to begin in Geneva Jan. 25, but held out little optimism for their success.

U.S. officials acknowledged the Saudi-Iran diplomatic rift diminishes chances for the peace process. "It's going to make it a lot harder," said an official who spoke on condition of anonymity.

"It's obviously very fragile," said a second senior U.S. official.

ARMS SALES MOVING FORWARD

Current and former U.S. officials said they believed Riyadh and Washington have too many shared interests, from ensuring the flow of oil, to fighting al Qaeda and Islamic State militants and completing huge arms contracts, to permit a fundamental breach.

U.S. and Saudi officials are continuing to work on a $1.29-billion sale of U.S. precision munitions approved in November, according to military and industry sources. The deal, which seeks in part to replenish bombs and missiles used in the Saudi battle against Iranian-backed Houthi rebels in Yemen, should be finalized in coming months.

A separate, $11.25-billion Saudi purchase of four Lockheed Martin Corp (LMT.N) surface warships, approved in October, also is expected to move forward on its years-long schedule, the sources said.

"The Saudi-U.S. defense relationship is a juggernaut," said Michael Knights, a fellow at the Washington Institute for Near East Policy think tank. "It survives endless presidents and kings and it just keeps rolling and that's what's going to happen this time."

LOOKING PAST OBAMA?

Despite the Saudis' ultimate reliance on U.S. security guarantees, the kingdom in the last year repeatedly has signaled a willingness to act independently of the U.S. on national security matters. Saudi Arabia gave the U.S. scant notice last March when, with Arab allies, it launched air strikes in Yemen against Houthi rebels it said are supported by Iran.

And last month, the kingdom announced the formation of a 34-nation Islamic military coalition to combat terrorism. The United States is not among the members.

Riyadh has also made little secret of its opposition to Obama�s nuclear deal with Iran, a hallmark of the U.S. president's foreign policy.

With Obama in his last year as president, Saudi Arabia seems to be looking past Obama, toward the next U.S. president, said one analyst with deep ties to Saudi officials.

"There are no expectations left with this administration," said Nawaf Obaid, a visiting fellow at Harvard University�s Belfer Center for Science and International Affairs. "Things will start from zero once he (Obama) leaves."

By Reuters