U.S. officials believed that Israel might have been plotting to kill Iran’s top negotiators while Washington was engaged with Tehran in delicate talks this spring to reach an interim peace deal, according to current and former American officials. Killing senior Iranian leaders had been part of Israel’s strategy from the start of the war. But American concerns about the targeting of two particular Iranian officials — Abbas Araghchi, Iran’s foreign minister, and Mohammad Bagher Ghalibaf, the speaker of the Parliament — spiked during delicate cease-fire negotiations that began in April. Fearful that an Israeli assassination effort would doom the negotiations,...