A four-week United Nations conference reviewing the treaty to prevent the spread of nuclear weapons ended on Friday without agreement as the United States and Iran sparred over Iran’s nuclear programme.

Vietnam’s UN Ambassador Do Hung Viet, who chaired the conference, announced that there was no consensus among the 191 parties to the Nuclear Nonproliferation Treaty on even a watered-down final document. He did not say which country or countries blocked a consensus.

It was the third failure in a row at a conference reviewing the NPT, considered the cornerstone of global non-proliferation and disarmament. 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.

Tensions over Tehran’s nuclear programme escalated ahead of the Iran war, which began with US and Israeli air strikes on February 28. President Donald Trump has said the war was aimed at preventing Iran from developing a nuclear weapon. Iran has enriched uranium to near weapons-grade levels but insists its programme is only for civilian purposes.

The US and Iran have clashed since the opening of the review conference on April 27. The US has accused Iran of showing “contempt” for its commitments under the treaty, while Iran has said US 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 UN nuclear watchdog agency. But Iran has not given inspectors from the International Atomic Energy Agency access to nuclear sites that were bombed by the US last June.