Washington's fear is that a Sunni-Shiite sectarian war could derail a number of US initiatives. Those include closer ties between Iraq and its security forces, as well as the Syrian peace efforts.
The Obama administration tread warily Monday around inflamed tensions between Iran and Saudi Arabia that threaten several key US foreign policy objectives.
A US official said Secretary of State John Kerry had spoken on Sunday with Iranian Foreign Minister Mohammad Javad Zarif, while the official Saudi Press Agency reported that Kerry had spoken on Monday with Saudi Deputy Crown Prince Salman.
Kerry is also due to make a round of calls Monday to the foreign ministers of all the Sunni-led states in the Persian Gulf region, including Bahrain, Kuwait, Qatar, the United Arab Emirates and Oman, the US official said. Bahrain followed Saudi Arabia's lead and severed diplomatic ties with Iran, while the UAE downgraded its diplomatic relations with it.
The US official said Kerry's message was to urge calm and warn against overreaction that some fear could lead to a sectarian war between Sunni-led Saudi Arabia and Shiite-ruled Iran.
Saudi Arabia's deputy crown prince Mohammed bin Salman has implemented a more aggressive foreign policy
US officials said the administration was loath to insert itself into the row between Riyadh and Tehran but wants to ensure the viability of the fight against the self-styled "Islamic State" group in Iraq and Syria, nascent attempts to end Syria's civil war, and the Iran nuclear deal.
Several officials said one of Washington's primary and most immediate concerns was the potential effect the spat could have on the fragile cooperation in Iraq between the Iraqi security forces, which answer to an Iran-friendly government, and Sunni and Shiite militias that are fighting Islamic State extremists.
Syrian peace talks at risk
Also of concern is the state of the Syrian peace effort, which is supposed to swing into high gear in late January with UN-sponsored negotiations between Saudi-backed opposition forces and the Iranian-supported government of Syrian President Bashar al-Assad.
UN Secretary General Ban Ki-moon expressed his dismay at the escalating tensions across the Persian Gulf via his spokesman.
"The Secretary-General reiterated that the attack on the Saudi embassy in Tehran was deplorable, but added that the announcement of a break in Saudi diplomatic relations with Tehran was deeply worrying," Ban's spokesman Stephane Dujarric said.
In Germany, the leader of the government's left-of-center party - the Social Democrats – renewed calls for the country to limit its military weapons sales to Saudi Arabia.
"We must now check whether we have to be more critical in future judgments on defensive arms goods," said Economy Minister Sigmar Gabriel, "which, up until now, we have delivered to Saudi Arabia to aid its national defense."
bik/msh (AP, Reuters)