After a long stalemate in talks aimed at dismantling its nuclear program, North Korea (search) may be sending a message to the world.
U.S. satellites have detected activity suggesting the reclusive communist country is preparing to test a nuclear weapon (search) for the first time, a senior U.S. official told FOX News. The apparent preparations for a test have been observed for months at Gilju (search), a suspected testing site in the country's northeast.
A heightened buzz in activity at the site, coupled with the construction of what looks to be an official reviewing stand, could mean the country is getting serious about proving the might of its weapons of mass destruction.
Still, U.S. officials have long known that North Korea was capable of testing a nuclear weapon with little warning, and many suspect what is happening at Gilju is just more pomp and bluster.
"Are we seeing what they want us to see and not seeing something else?" one Defense Department official wondered.
After all, officials told FOX News, the North Koreans know when they are being monitored by American spy satellites. (The United States does not have enough to keep an eye on the country at all times.)
U.S. officials said they were monitoring the developments, which were detailed in a report by the New York Times on Friday.
"We certainly don't have any new assessment of North Korea's nuclear program," State Department spokesman Tom Casey said.
"We are still focused on getting North Korea back to the table for the six-party talks," Casey continued. "We believe that anything North Korea does that takes it further away from bringing those talks back on line only serves to isolate it [and] hurt the interests of North Korea and its people."
The impoverished regime angrily walked away from talks on its nuclear ambitions with Washington, neighbor South Korea, Japan, China and Russia nearly a year ago, insisting on two-way negotiations with the United States, which it blamed for the crisis.
Last week, a top Pentagon official told Congress he believes Pyongyang is now able to place a nuclear warhead on a long-range missile capable of reaching the United States.
The satellite images show the North Koreans have dug and refilled a significant hole at Gilju, one Defense official said on condition of anonymity. The hole was dug in a manner consistent with preparations for an underground nuclear test, although it is not known whether a weapon was deposited inside, the official said.
In addition, they have built some bleachers a sufficient distance from the opening, presumably for officials to view a test, the official said.
While the country's penchant for hyperbole led some observers to be skeptical it would actually test a weapon, others reiterated long-standing criticisms that the Bush administration has badly fumbled the nuclear standoff.
"The evidence is not definitive, but it suggests a nuclear test may be on the way, and this would be consistent with North Korea's actions throughout this crisis," Ted Galen Carpenter, author of "The Korean Conundrum" (search), told FOX News.
"They have done everything they have threatened to do and they have proceeded in a very rigorous way to develop nuclear weapons. I think the U.S. has underestimated the nature of this crisis," Carpenter said.
Although North Korea has claimed it has nuclear weapons, and U.S. intelligence agencies believe it, a test would confirm the extent of their capabilities.
Separately, a senior Japanese Defense Agency official told The Associated Press that Japan's government had information that North Korea might be preparing for a nuclear test.
Japan threatened on Friday to put North Korea's nuclear weapons program before the U.N. Security Council next month unless six-nation talks on the dispute show progress.
There have been several recent reports of apparent planning for a possible test. The New York Times reported Friday that the U.S. government has informed Japan and South Korea about the satellite imagery. On Tuesday, South Korea's mass-circulation Chosun Ilbo reported that U.S. satellite photos showed the frequent movement of trucks and the placement of cranes and other equipment at Gilju.
FOX News' Jane Roh and The Associated Press contributed to this report.