The argument was reportedly so intense that a Kerry aide “tip-toed into the room” to remind the men that everyone in the building could hear them shouting.

Zarif has lashed out at Western negotiators on many occasions.

The foreign minister reportedly “erupted” at E.U. negotiator Federica Mogherini when she mentioned Iran’s role in destabilizing the Middle East. Iran has stoked conflict in Syria, Yemen and other countries by funding Islamist terror groups like Hezbollah.

“Never try to threaten the Iranians,” Zarif yelled on another occasion when it was mentioned that the P5+1 could end the nuclear talks because of Iranian intransigence.