"Well, at some point, presumably, if there's going to be any engagement on this, that would have to require diplomacy. That's what we're in the business of."
Iran in January said it has resumed 20% uranium enrichment at its underground Fordow nuclear site, well above the deal's limit but far short of the 90% that is weapons-grade.
The gathering coincided with increasing tensions between Iran and the United States in the last days of President Donald Trump's administration, and many in the crowd demanded revenge.
"Be careful of a trap, @realDonaldTrump. Any fireworks will backfire badly, particularly against your same BFFs," Zarif wrote, in what appeared to be a veiled threat against Israel.
U.S. officials blame Iran-backed militia for regular rocket attacks on U.S. facilities in Iraq, including near the embassy. No known Iran-backed groups have claimed responsibility.