The Obama administration disclosed the size of its atomic stockpile going back to 1962 as part of a campaign to get other nuclear nations to be more forthcoming, and to improve its bargaining position against the prospect of a nuclear Iran.

"We think it is in our national security interest to be as transparent as we can be about the nuclear program of the United States," Secretary of State Hillary Rodham Clinton told reporters at the United Nations, where she addressed a conference on containing the spread of atomic weapons.

The US has previously regarded such details as top secret.

The figure includes both "strategic," or long-range weapons, and those intended for use at shorter range.

The Pentagon said the stockpile of 5,113 as of September 2009 represents a 75 percent reduction since 1989.