President Bush has approved "a significant reduction" in the U.S. nuclear weapons stockpile, cutting it to less than one-quarter its size at the end of the Cold War, the White House said Tuesday.

"We are reducing our nuclear weapons stockpile to the lowest level consistent with America's national security and our commitments to friends and allies," White House press secretary Dana Perino said. "A credible deterrent remains an essential part of U.S. national security, and nuclear forces remain key to meeting emerging security challenges."

The government will not provide any numbers on the overall size of the nuclear stockpile, but there are believed to be nearly 6,000 warheads that either are deployed or in active reserve.

Under terms of a 2002 arms control treaty with Russia, the U.S. is committed to reducing the number of deployed warheads to between 1,700 and 2200 by 2012.

Three years ago, Bush said he wanted the overall stockpile reduced to half of what it was in the 1950s, or to a level of about one-quarter of its size at the end of the Cold War.