Tensions between Saudi Arabia and Iran are not only threatening regional stability but also present a challenge for the U.S., as it tries to help resolve other conflicts in the area and gain more traction in the fight against ISIS.
After Saudi Arabia executed a prominent Shiite cleric, protesters stormed the Saudi Arabian embassy in Tehran, and soon after, Saudi Arabia severed diplomatic ties with Iran. The United Arab Emirates (UAE), an ally of Saudi Arabia, also downgraded diplomatic ties, and protests also ensued in Turkey and Bahrain.
"What you have is a conflict that has been enduring for some time that has really come to a head, and now you have a flash point," said CBS News Senior National Security Analyst Juan Zarate. "The challenge here -- not just for the United States, but for the rest of the world -- is that this is not going to go away."
Even if the two countries are able to get beyond this spat, Zarate says that they're essentially "at war with each other, and they're going to do it via proxies."
Saudi Arabia is the predominant Sunni power in the region, while Iran represents the Shiite center. The two countries are already involved in proxy wars in both Yemen and Syria, but this recent rift between Riyadh and Tehran is beginning to threaten the U.S. ability to manage other volatile conflicts in the region.
Tensions are also spiking in Bahrain, where a Shiite majority is already pushing back against the wealthier and more powerful Sunni leadership that is allied with Saudi Arabia. It's a strategically important country for the U.S., since about 5,000 Marines and sailors are stationed there with the U.S. Navy's 5th Fleet.
"Unless Saudi-Iranian tensions abate, Washington has no chance of winning the war against [the Islamic State of Iraq and Syria] or ameliorating sectarian tensions in Iraq or Syria. Right or wrong, the Saudis are going their own way. The U.S. will be left to pick up the pieces," Wilson Center scholar Aaron David Miller wrote in the Wall Street Journal recently.
The two nations are both scheduled to attend peace talks to resolve the Syrian conflict in Geneva on Jan. 25, and both say they still plan to attend.
But the war of words between the two nations continued Sunday with Iranian Foreign Minister Mohammad Javad Zarif authoring a blistering op-ed in the New York Times Sunday accusing Saudi Arabia of acting out in response to the Iran nuclear deal and the "fear that its contrived Iranophobia was crumbling." He went on to argue that Saudi Arabia was fomenting that fear to undermine the deal and distract from its sponsorship of violent extremism.
"The Saudi leadership must now make a choice: They can continue supporting extremists and promoting sectarian hatred; or they can opt to play a constructive role in promoting regional stability."
U.S. officials have been wary of chosing sides. They are working to implement the Iran deal, but are also counting on Saudi Arabia and its Sunni allies to serve as the ground force in the fight against ISIS.
"The U.S. wants to calm the tensions. They don't want to see an exacerbation of any of these conflicts that we're talking about, and they certainly don't want to see extremist groups advantaged by this," Zarate said. "They don't want to see Sunni extremist groups getting more support from Saudi Arabia or Qatar or the UAE because they are seen as proxies to fight against Iran, so the U.S. has an interest in dampening this tension."
White House spokesman Josh Earnest said last week that there's "plenty of blame to go around," and urged both sides to deescalate tensions.
State Department spokesman John Kirby was a little more blunt. "If you're asking if we're trying to be a mediator in all this, the answer is no," he told reporters earlier this month.
One challenge, Zarate said, is that the U.S. has lost credibility in the region in recent years. He maintained that the Saudis are listening to the U.S. less than they used to.
"They see the Iran nuclear deal as a demonstration that the U.S. is now siding a bit with the Iranians," Zarate said. He also pointed to the U.S. failure to act after Syrian President Bashar Assad used chemical weapons on his own people.
"They don't trust the United States as they once did. And so in a sense, Saudis are going to go at it alone. And we've seen that in Yemen, we're seeing it here, and we can tell them what we want, and we can ask them to do what we want," Zarate said, "but they see themselves as in a battle for influence with Iran, and they're not sure the U S. going to be there with them," he said.