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.