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  (Reuters/Kim Kyung-Hoon)
  North (R) and South Korean soldiers stand guard.

North Korea is apparently planning a nuclear test, according to South Korean intelligence officials. Satellite imagery shows an underground tunnel that may be a part of its nuclear site testing.

"North Korea is covertly preparing for a third nuclear test, which would be another grave provocation," said a report by South Korean officials. "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."

North and South Korea have been at odds for years, and a new missile test by North Korea could set off a chain of events that would lead to more war. Last month, North Korea announced plans to launch a three-stage rocket in mid-April to commemorate the 100th birthday of Kim-il Sung.

World leaders, including those in South Korea and the United States have urged North Korean officials not to conduct more nuclear tests. Even China, North Korea's greatest ally has voiced concern for the missile launch.

"China strongly encourages everyone involved to remain calm and reasonable. These issues need to be worked out in a diplomatic and peaceful manner," Chinese foreign minister Yang Jiechi told Chinese news agency Xinhua.

"If you look for yourselves with your own eyes, then you can judge whether it's a ballistic missile, or whether it's a launch vehicle to put a satellite into orbit," Jang Myong Jin, head of the launch site, told CNN. "That's why we've invited you to this launch site."

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South Korean officials are wary of reports coming from North Korean leaders. "

Once again this shows … they know how to manipulate the world. If they do a missile launch and in a few months a successful nuclear test, especially a uranium based nuclear device, it will send a very strong message to the world," said Andrei Lankov of Seoul's Kookmin University.

"The same message they always want to deliver- we are here, we are dangerous, unpredictable and it's better to deal with us by giving us monetary and food concessions," Lankov told CNN.