NEW YORK CITY — A four-week United Nations conference reviewing the treaty to prevent the spread of nuclear weapons ended Friday without agreement among its 191 parties. Vietnam's U.N. Ambassador Do Hung Viet, who chaired the conference, announced that there was no consensus on even a watered-down final document.

The review conference opened on April 27 and ended on May 22, 2026. Do Hung Viet did not say which country or countries blocked consensus. It was the third failure in a row at a conference reviewing the Nuclear Non-Proliferation Treaty. At the last treaty review in August 2022, Russia blocked agreement on a final document over its February 2022 invasion of Ukraine and references to Moscow's occupation of the Zaporizhzhia nuclear power plant, Europe's largest.

The United States and Iran have clashed since the opening of the review conference on April 27. The U.S. accused Iran of showing "contempt" for its commitments under the treaty. Iran said U.S. and Israeli attacks on its nuclear facilities violated international law.

Iran is a party to the NPT, which requires countries to open all nuclear sites to inspection by the U.N. nuclear watchdog agency. Iran has not given inspectors from the International Atomic Energy Agency access to nuclear sites that were bombed by the U.S. last June. Iran has enriched uranium to near weapons-grade levels but insists its program is only for civilian purposes.

Tensions over Tehran's nuclear program escalated ahead of the Iran war, which began with U.S. and Israeli airstrikes on Feb. 28, 2026. President Donald Trump said the war was aimed at preventing Iran from developing a nuclear weapon.

In speeches at the end of the conference, the U.S. called Iran a "prolific treaty violator" and said Iran had spent the conference "shirking accountability for its grotesque violations." Iran accused the U.S. and its allies of conducting a "relentless campaign" to legitimize their "unlawful attacks" on the country and its nuclear facilities.

"The conference showed that rhetorical support for the NPT is strong, but the foundations of the NPT are cracking due to inaction, inattention, and intransigence on the part of the major powers," said Daryl Kimball, Executive Director of the Arms Control Association. "Much more enlightened, engaged, and pragmatic leadership and diplomacy will be needed to guard against the growing risks of an unconstrained nuclear buildup, threats to resume nuclear testing, and the risk of a nuclear-armed Iran," Kimball added.

"U.S. and Russia double down on nuclear threats, blame others and try to undermine or ignore the NPT's nuclear disarmament commitments and related agreements," said Rebecca Johnson, Founding Executive Director of the Acronym Institute for Disarmament Diplomacy.