The US has revealed it has 5,113 nuclear warheads in stockpile.This is the first time the Pentagon has officially disclosed the number after previously regarding the information as top secret.A senior defence official said the size of the stockpile represents a 75% reduction since 1989.“Increasing the transparency of global nuclear stockpiles is important to non proliferation efforts,” said a statement from the Pentagon.The US government last disclosed details of the stockpile in 1993, releasing figures current up to 1961.The total does not include warheads that have been retired and scheduled for dismantlement – an estimated 4,600 according to the Federation of American ScientistsgroupThe release coincides with Secretary of State Hillary Clinton’s address to the United Nations nuclear Non-Proliferation Treaty (NPT) review conference.It is checking up on efforts to contain the spread of nuclear weapons around the world.Mrs Clinton accused Iran of “flouting the rules” and called for a strong international response to Tehran’s alleged development of a nuclear weapons program.She added that Iranian President Mahmoud Ahmadinejad would fail in his bid to wreck the NPT review conference, currently taking place in New York.“It appears that Iran’s president came here today with no intention of improving the NPT,” Clinton told a press conference after her speech to delegates to the conference.“He came to distract attention from his own government’s failure to live up to its international obligations, to evade accountability for defying the international community and to undermine our shared commitment to strengthening the treaty,” she said.“But he will not succeed.”Earlier the Iranian President had addressed the conference and denounced the Obama administration’s refusal to rule out the use of U.S. nuclear weapons.“Regrettably the government of the United States has not only used nuclear weapons but also continues to threaten to use such weapons against other countries, including Iran,” Ahmadinejad said.As he spoke, the U.S. delegation walked out of the General Assembly hall, as did several European delegations including the French and British.The NPT is regarded as the world’s single most important pact on nuclear arms.It is credited with preventing their proliferation to dozens of nations since it entered into force in 1970.