NEW YORK, Sept. 24 -- When Masoud Pezeshkian walked to the podium of the United Nations General Assembly on Wednesday, he carried something unusual: photographs. One showed Ayatollah Ali Khamenei, Iran's supreme leader, killed in a joint US-Israeli strike last February. Others showed more than 150 Iranian schoolchildren who died in the opening days of the war, alongside photographs of their graves.

He held them up before the assembled delegates and said nothing for a moment.

Then: "Is this how the world's most powerful country practises international law?"

The question landed in a hall that had heard, the day before, Donald Trump stand at the same podium and threaten to "annihilate" Iran if a deal was not reached soon. The two speeches...