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Relations between Iran and Saudi Arabia have always been thorny, but rarely has the state of affairs been as venomous as it is today.

Tehran and Riyadh each point to the other as the main reason for much of the turmoil in the Middle East. In its most recent incarnation, the Iranian-Saudi conflict by proxy has reached Yemen in a spiral that both sides portray as climatic.

For Riyadh and its regional allies, the Saudi military intervention in Yemen -- "Operation Decisive Storm" -- is the moment the Sunni Arab nation finally woke up to repel the expansion of Shia-Iranian influence.

For Tehran and its regional allies -- including the Houthi movement in Yemen -- Saudi Arabia's actions are in defense of a retrogressive status quo order that is no longer tenable. And yet both sides have good reasons to want to stop the Yemeni crisis from spiraling out of control and evolving into an unwinnable war.

Syria, Iraq and now Yemen

When Iranian President Hassan Rouhani was elected in June 2013, he pledged to reach out to Riyadh. He was up front and called Tehran's steep deterioration of relations with the Saudis over the last decade as one of the principal burdens on Iranian foreign policy. From Lebanon and Afghanistan to Pakistan and the Gaza Strip, the Iranian-Saudi rivalry and conflict through proxy has been deep and costly.

And yet despite Rouhani's open pledge, profound differences over Syria and Iraq in particular have kept Riyadh and Tehran apart. But if the questions of Syria and Iraq prevented a pause in hostilities, the Saudi military intervention in Yemen since late March has all but raised the stakes to unprecedentedly dangerous levels. Unlike in Syria and in Iraq, the Saudi military is now directly battling it out with Iranian-backed rebels in Yemen.

While Riyadh no doubt exaggerates Tehran's role in the Yemen crisis, its fingerprints are nonetheless evident.