WASHINGTON -- The Obama administration tread warily Monday around inflamed tensions between Iran and Saudi Arabia that threaten several key U.S. foreign policy objectives.

The White House said Secretary of State John Kerry had spoken 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 Mohammed bin Salman.

U.S. officials said the administration is loath to insert itself into the row between Riyadh and Tehran but wants to ensure the viability of the fight against the Islamic State group in Iraq and Syria, nascent attempts to end Syria's civil war and the Iran nuclear deal.

White House spokesman Josh Earnest called on both countries to show restraint and avoid further inflaming sectarian tensions between Sunni-led Saudi Arabia and Shiite-ruled Iran. And he urged Saudi Arabia and Iran not to let the conflict derail fragile talks aimed at securing a cease-fire and a political transition to end the war in Syria.

"Hopefully they will continue to engage," Earnest said. "It is so clearly in the interests of both countries to advance a political solution to the situation inside of Syria."

Kerry is also planning 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, officials said. Bahrain followed Saudi Arabia's lead and severed diplomatic ties with Iran, while the UAE downgraded its diplomatic relations with it. In addition to Kerry, other senior U.S. diplomats were in close contact with Saudi and Arab officials over the weekend, according to the U.S. officials who spoke on condition of anonymity because they were not authorized to speak publicly to the delicate diplomacy.

The U.S. message to all is to urge calm and warn against overreaction that some fear could lead to a sectarian war, officials said.

Several officials said one of Washington's primary and most immediate concerns is the potential effect the spat could have on the fragile co-operation 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. That co-operation has shown gains in recent weeks, notably with the Iraqi recapture of the provincial capital of Ramadi from the Islamic State group.

Officials were preparing for a high-level U.S. conversation with Iraqi Prime Minister Haider al-Abadi to stress the importance of continuing the Iraqi government's outreach to Sunni militias, the officials said.

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 Assad. A U.S. official said Kerry had spoken on Sunday with the U.N special envoy for Syria, Staffan de Mistura, to gauge any impact Saudi-Iranian developments might have on the planned Jan. 25 start of negotiations. There was no immediate indication that those talks would be disrupted, the official said.

Meanwhile, the United Nations said de Mistura will head to Saudi Arabia and Iran this week to try to ensure the talks go ahead.

UN deputy spokesman Farhan Haq said de Mistura "hopes that the adverse consequences of the tensions between Saudi Arabia and Iran do not affect the peace process with the Syrians."