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Iranians gather during a demonstration against the execution of prominent Shiite Muslim cleric Nimr al-Nimr by Saudi authorities, at Imam Hossein Square in the capital Tehran on January 4, 2016. Tensions between Iran and its Sunni Arab neighbours reached new heights as Saudi Arabia and Gulf allies cut or downgraded diplomatic ties with Tehran in a row over the execution of a Shiite cleric. AFP PHOTO / ATTA KENARE / AFP / ATTA KENARE        (Photo credit should read ATTA KENARE/AFP/Getty Images)
Iranians gather during a demonstration against the execution of prominent Shiite Muslim cleric Nimr al-Nimr by Saudi authorities, at Imam Hossein Square in the capital Tehran on January 4, 2016. Tensions between Iran and its Sunni Arab neighbours reached new heights as Saudi Arabia and Gulf allies cut or downgraded diplomatic ties with Tehran in a row over the execution of a Shiite cleric. AFP PHOTO / ATTA KENARE / AFP / ATTA KENARE        (Photo credit should read ATTA KENARE/AFP/Getty Images)

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    Why can't Iran and Saudi Arabia get along?

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Why can't Iran and Saudi Arabia get along?

CNN's Fred Pleitgen explains what's behind the diplomatic row between Saudi Arabia and Iran, and why the relations between the two are so complicated.

Why can't Iran and Saudi Arabia get along?

CNN's Fred Pleitgen explains what's behind the diplomatic row between Saudi Arabia and Iran, and why the relations between the two are so complicated.