Ambassador Majid Takht Ravanchi cited progress in achieving a universal ban on nuclear explosions and the broader objective of nuclear disarmament but said "unfortunately, currently, there are two alarming races: new nuclear arms race and nuclear arms modernization race."
He told Monday's U.N. General Assembly's commemoration of the International Day Against Nuclear Tests that "irresponsible policies" like those of the U.S. "are detrimental to all international efforts towards nuclear disarmament and non-proliferation, and therefore must come to an end."
Ravanchi stressed that voluntary moratoriums on nuclear testing "cannot substitute for a comprehensive universal and verifiable legally binding prohibition on all types of nuclear explosions, including in alternative ways."
He urged redoubled effort to pursue "the noble objective of the total elimination of nuclear weapons."
China has blamed the United States for tensions over Iran's nuclear program and called for world powers to stick to their 2015 deal with Tehran.
Foreign Ministry spokeswoman Hua Chunying said Monday: "The U.S. should abandon wrong practices such as unilateral sanctions and maximum pressure on Iran."
The deal started collapsing with the United States unilaterally withdrawing last year and imposing sanctions on Iran.
The Chinese ministry spokesman says parties to the deal, which also include Britain, France, Germany, China, Russia and the European Union — should stay committed to all parts of the comprehensive agreement.
Her comments followed Iran's announcement that it would start using advanced centrifuges that are prohibited under the agreement. The centrifuges can be used to enrich uranium.
Iran is trying to pressure Europe to find a way to ease the economic toll of the sanctions.
The United Nations' atomic watchdog is confirming Iran is moving ahead with preparations to start using more advanced centrifuges, in breach of limitations set in the unraveling 2015 nuclear deal with major powers.
The International Atomic Energy Agency said Monday its inspectors verified new centrifuges, including 30 advanced IR-6 and three IR-6s models, had been or were being installed but not yet tested.
The announcement followed the return from Tehran Sunday of IAEA Acting Director General Cornel Feruta.
A centrifuge enriches uranium by spinning uranium hexafluoride gas. Under the atomic accord, Iran's currently limited to operating 5,060 older IR-1 centrifuges.
Iran had announced the move, its latest breach of the nuclear deal as it tries to pressure Europe to find a way to sell crude oil abroad despite U.S. sanctions.