Recent satellite images show North Korea is digging a new underground tunnel in what appears to be preparation for a third nuclear test, according to South Korean intelligence officials.
The excavation at North Korea's northeast Punggye-ri site, where nuclear tests were conducted in 2006 and 2009, is in its final stages, according to a report by intelligence officials that was shared Monday with The Associated Press. Its release comes as North Korea prepares to launch a long-range rocket that Washington and others say is a cover for testing missile technology that could be used to fire on the United States.
Observers fear a repeat of 2009, when international criticism of the North's last long-range rocket launch prompted Pyongyang to walk away from nuclear disarmament negotiations and, weeks later, conduct its second nuclear test. A year later, 50 South Korean were killed in attacks blamed on the North.
"North Korea is covertly preparing for a third nuclear test, which would be another grave provocation," said the report, which cited U.S. commercial satellite photos taken April 1. "North Korea is digging up a new underground tunnel at the Punggye-ri nuclear test site, in addition to its existing two underground tunnels, and it has been confirmed that the excavation works are in the final stages."
Dirt believed to have been brought from other areas is piled at the tunnel entrance, the report said, something experts say is needed to fill up underground tunnels before a nuclear test. The dirt indicates a "high possibility" North Korea will stage a nuclear test, the report said, as plugging tunnels was the final step taken during its two previous nuclear tests.
North Korea announced plans last month to launch an observation satellite using a three-stage rocket during mid-April celebrations of the 100th anniversary of the birth of North Korean founder Kim Il Sung.
The U.S., Japan, Britain and other nations have urged North Korea to cancel the launch, warning that firing the long-range rocket would violate U.N. resolutions and North Korea's promise to refrain from engaging in nuclear and missile activity.
Pyongyang says the rocket will only carry a weather satellite, but South Korea and the United States say it is a test of a ballistic missile. And although the risk of it veering off course is low, guidance remains its weakest point.
In a rare move, reporters -- including NBC News' Richard Engel -- were taken to the new Sohae launch station, close to the border with China, where work was in progress to ready the 100-foot high Unha-3 rocket and its satellite.
The three-stage rocket was on the launch platform, indicating the launch is likely between April 12-16.
"Supreme Commander Kim Jong Un made a very bold decision, that is why you are allowed to be this close to the launch site," site director Jang Myong Jin told visiting foreign journalists on Sunday.
However, NBC's Engel tweeted that North Korea seemed to be giving the press access "to deflect criticism against the rocket launch, to show it has nothing to hide."
The second stage booster is planned to separate in the seas to the west of the Philippines, about 1,860 miles from the launch site, and experts say that represents the first possible landfall for the rocket if things go wrong.
North Korea will launch what is being described as a small observation satellite within days.
If North Korea does achieve a successful separation of the third stage -- something it says it achieved in 2009, but most experts say failed to put a previous satellite into orbit -- that would show it had improved its technology and the capacity to produce a missile that could carry an intercontinental nuclear warhead. Pyongyang has also shifted its launch site, and the new, more sophisticated site on the west of the Korean peninsula reduces the risk of debris falling on Japan, which was overflown in a previous test-launch of a missile.
The new rocket is believed to have a design range of more than 4,160 miles, and can carry a payload of up to 2,204 pounds.
At its closest point, Alaska in the United States is about 3,100 miles from North Korea.
While North Korea's 23 million people live in poverty and many are at risk of malnutrition, the prestige of developing rocket technology and nuclear weapons capacity is the most important issue for Pyongyang, which sees it as a deterrent against invasion.
The North is believed to have stockpiled enough fissile material to manufacture up to 10 nuclear bombs.
Government officials in South Korea have calculated the North is spending $19 million on this launch.