U.S. spy satellites show North Korea  could be moving toward making nuclear warheads, U.S. officials said, as a top military commander called for more troops, bombers and ships to bolster ally South Korea . In a sign the crisis on the Korean peninsula is deepening, U.S. officials said on Friday the satellite images show North Korean workers moving fuel rods around a key nuclear complex, including possibly some of the 8,000 spent fuel rods.

The spent rods can be reprocessed to extract plutonium, the fuel used in atomic warheads, although there was no sign reprocessing had begun after a month of furious activity at the Yongbyon reactor site, the officials said.

"Any steps toward beginning reprocessing would be yet another provocative action by North Korea intended to intimidate and blackmail the international community," U.S. presidential spokesman Ari Fleischer  told reporters.

He declined to comment on a New York Times report that the stockpile of 8,000 spent fuel rods was being moved.

Weapons experts say the North would cross a red line and show it was determined to build bombs should it begin to reprocess the spent rods. The experts say the North could build six warheads from plutonium extracted from this batch of rods.

With the U.S. edging closer to war in Iraq, Admiral Thomas Fargo, based in Hawaii as commander of all American forces in Asia and the Pacific rim, had asked for reinforcements to send the North a message that the U.S was prepared for any contingency, U.S. officials said.

The reinforcements include several thousand more troops to bolster the 37,000 already based in South Korea, along with B-1 and B-52 bombers and possibly an aircraft carrier.

"The admiral wants to be sure that the North Koreans don't launch any adventure to take advantage of what they might see as preoccupation with Iraq," said one defense official. "He feels it would be a prudent step."

"ATMOSPHERE OF WAR"

"There is still activity around Yongbyon, some of it associated with the reactor, an immediate thing that's not as bad as reprocessing but still isn't good," a senior U.S. official told Reuters.

"I don't discount that they might begin reprocessing in the next month, or do another missile launch," but there were no signs of preparations for such a test, the official said, referring to a missile test-fired over Japan in 1998.

There was no immediate reaction from Pyongyang to the U.S. intelligence report or the request for U.S. reinforcements, but the North's Korean Central News Agency said U.S. surveillance and military exercises were "inciting a war atmosphere."

"All the aerial espionage flights and aerial war exercises saliently reveal the hypocrisy of the U.S. talk about 'non- aggression on North Korea' and 'dialogue' allegedly to seek a 'peaceful settlement' of the nuclear issue on the Korean peninsula," KCNA said.

If confirmed, moves by North Korea to launch production of nuclear weapons would mark a major step in the nuclearization of North Asia, where nuclear-armed China fears Japan might develop the weapons in response to North Korea's possession of them.

South Korea said on Saturday it had not confirmed the latest U.S. satellite intelligence and had not been informed of any U.S. request to augment its troops in the South.

The Korean crisis was sparked last October when the United States said Pyongyang had admitted to developing a highly enriched uranium program in violation of a 1994 accord. Under that pact, the North froze its nuclear program in exchange for two nuclear energy reactors and economic assistance.

Pyongyang expelled U.N. nuclear inspectors and removed seals from reactor at Yongbyon in December. Last month, the North pulled out of the treaty preventing the spread of nuclear arms.

BUSTLING WITH ACTIVITY

Even as they try to keep the North Korea crisis on a diplomatic track, Bush administration officials seem increasingly convinced that Pyongyang is determined to launch full-scale production of nuclear weapons.

Another official told Reuters Yongbyon was "bustling with activity. There are canisters and vehicles moving about. It's hard to rule in or out that spent fuel rods are on the move but it's certainly plausible."

U.S. officials in recent weeks have detected North Korea had moved quantities of fresh fuel rods to the area of a nuclear reactor at Yongbyon. It is in the reactor where the unused uranium fuel rods are converted to plutonium.

An even more significant step would be for Pyongyang to move the 8,000 spent fuel rods -- which have already gone through the reactor -- from a holding pond where they had been mothballed under the 1994 agreement.

Fresh fuel rods "probably" have been moved at Yongbyon and spent fuel rods "possibly" have been moved, said one official, noting that intelligence was not clear-cut.

Another official, who initially said he believed the spent fuel rods were still in the cooling pond, later amended his comment, saying: "We don't know" where they are.

U.S. intelligence estimates North Korea produced enough plutonium for one to three nuclear weapons before the Yongbyon facility was mothballed in 1994.

PHOTO CAPTION

This satellite image of the Yongbyon facility in North Korea was captured by DigitalGlobe's QuickBird satellite on March 2, 2002. U.S. spy satellites show North Korea is moving fuel rods around the key nuclear complex but there is no sign that reprocessing -- which is critical to making bombs -- has begun, U.S. officials said on January 31, 2003. (Digitalglobe via Reuter