The unnamed official, speaking to reporters on background, said the nation's nuclear arsenal stood at 5,113 warheads as of Sept. 30, down from a peak of 31,255 in fiscal 1967, the Armed Forces Press Service reported.
The information was part of newly declassified details the United States released as a signal of the country's interest in promoting transparency and helping limit nuclear proliferation. The release occurred the same day as representatives of governments around the world gathered at the United Nations in New York to begin a review of progress made under the Nuclear Non-Proliferation Treaty.
The defense official said the current total also is 75 percent lower than the 22,217 warheads the United States had in 1989 when the Berlin wall fell. He said 8,748 warheads were dismantled between fiscal 1994 and 2009, with thousands more retired and awaiting dismantlement.
"For those who doubt that the United States will do its part on disarmament, this is our record, these are our commitments," Secretary of State Hillary Rodham Clinton told the U.N. conference. "And they send a clear, unmistakable message."