Speaking on the second day of a two-week meeting of the 189 signatories of the pact, Assistant Secretary of State Rose Gottemoeller declined to say whether Washington would take any new steps to press Israel to join the treaty and give up any nuclear weapons it has.
Iran's Deputy Foreign Minister Mohammad Ali Hosseini on Monday railed against the United States and what he said was its continued nuclear support for the "Zionist regime". Western diplomats called this an attempt to divert attention away from its own nuclear program.
In failing to mention Iran even once in her speech, Gottemoeller broke from a tradition established by the administration of former President George W. Bush, which had used NPT meetings to criticize Iran and North Korea.
She also defended a US-India civilian nuclear deal, which developing nations have complained rewards New Delhi for staying outside the NPT.
Nuclear-armed India and Pakistan have never signed the treaty. North Korea withdrew from it in 2003 and tested a nuclear device in 2006.