President George W Bush has ordered a "significant reduction" in the US nuclear weapons stockpile, bringing it down to about one-quarter of its size at the end of the Cold War.
White House spokeswoman Dana Perino on Tuesday said the decision is meant to reduce US reliance on nuclear weapons for national security and modernize the nuclear programme.
"A credible deterrent remains an essential part of US national security, and nuclear forces remain key to meeting emerging security challenges," Perino said.
Experts believe the US has more than 5,000 nuclear warheads. The US is required in a treaty with Russia to reduce its warhead stockpile to under 2,200 by 2012.