North Korea 'building tunnel for third nuclear test'

North Korea is digging an underground tunnel in apparent preparation for a new nuclear test, intelligence reports have claimed.

Satellite handout showing a three-dimensional image of North Korea's suspected nuclear test site in P'unggye-yok Kilu county

Satellite images depict mounds of earth piled at the entrance of a tunnel at a site in northeast Punggye-ri, where two controversial nuclear tests were conducted in 2006 and 2009.

Observers fear that the creation of a new tunnel could indicate North Korea's intentions to conduct a third underground nuclear test, a move which would ignite widespread international criticism.

"North Korea is covertly preparing for a third nuclear test, which would be another grave provocation," said a report compiled by South Korean intelligence officers and obtained by The Associated Press.

"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."

Suspicions surrounding the possibility of a new nuclear test coincided with peaking regional tensions as North Korea counts down to this week's launch of an observation satellite using a three-stage rocket.

The reclusive state claims the rocket launch will peacefully mark the 100thanniversary of the birth of the North Korean founder Kim Il-sung, although the move is widely regarded in the international community as cover for a long-range ballistic missile test.

Japan, where the Prime Minister David Cameron is heading for a two-day visit this week, has stationed missile interceptors in southern Okinawa and the capital Tokyo, with top orders to shoot down any part of the rocket that enters its territory.

Meanwhile, North Korea took the unusual step of inviting foreign journalists into the secretive region in order to view its rocket launch site in a bid to convince the world of its argument that its intentions are peaceful.

During a visit to the site, the rocket was described as being painted white with sky-blue lettering, measuring 99 feet in height with a diameter of eight feet.

It will reportedly be accompanied by the Kwangmyongsong-3 (Shining Star) satellite, consisting of a 220 pound box with five antennae, powered by electricity generated by a covering of solar panels.

North Korean officials reportedly told media that the function of the satellite is to collect data on forests and natural resources across the region, with officials able to destroy it if it veers off route.

The world's eyes are fixed on North Korea this week less than four months after the still untested Kim Jong-un took over from his father and long-term ruler Kim Jong-il following his death in December.

Hundreds of thousands of residents are expected to fill the streets of North Korea's showpiece capital Pyongyang on Sunday to celebrate the centenary event marking the state founder's birth.