President Donald Trump on Thursday ruled out striking Iran with a nuclear weapon, after previous threats invoked rhetoric about destroying Iranian civilization.
"No, I wouldn't use it," Trump told reporters at the White House.
"Why would I use a nuclear weapon when we've, in a very conventional way, decimated them without it?" he asked. "A nuclear weapon should never be allowed to be used by anybody."
Trump on April 7 issued a stark threat that alarmed some critics. In it, he said that a "whole civilization will die tonight, never to be brought back," though within hours he agreed to a ceasefire that he has since extended.
Vice President JD Vance has himself warned that the United States is ready to intensify damage against Iran with weapons not previously used, but the White House has flatly denied he was threatening deployment of nuclear strikes.
Vance has been pressing Iran for greater concessions on its own contested nuclear work.
Trump told reporters that he was seeking an Iran "without a nuclear weapon that's going to try and blow up one of our cities or blow up the entire Middle East."
Iran denies seeking a nuclear weapon and the UN nuclear watchdog says that an atomic bomb was not imminent before the war. But many officials have voiced concern about Iran's efforts to enrich uranium, a key component of nuclear weapons.
The United States is the only country to have used nuclear weapons in combat, devastating the Japanese cities of Hiroshima and Nagasaki at the end of World War II and killing some 214,000 people.
Israel is widely known to have nuclear weapons but does not publicly acknowledge them.
U.S. nuclear doctrine has long reserved the right to use nuclear weapons.
Trump has previously called for an end to a U.S. moratorium on nuclear testing in response to suspicions of secret testing by China and Russia.
Former President Barack Obama had called for an eventual goal of a world without nuclear weapons, but his administration also said that so long as they existed, the U.S. arsenal would serve as a deterrent.
The United States has rejected calls to declare that it will never use nuclear weapons first in a conflict.