Recent satellite images show the Democratic People's Republic of Korea is digging a new underground tunnel in what appears to be preparation for a third nuclear test, according to intelligence officials from the Republic of Korea.

The excavation at the DPRK'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 the DPRK 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 DPRK's last long-range rocket launch prompted Pyongyang to walk away from nuclear disarmament negotiations and, weeks later, conduct its second nuclear test.

"(The DPRK) is covertly preparing for a third nuclear test, which would be another grave provocation," said the report, which cited US commercial satellite photos taken April 1. "(The DPRK) is digging 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" the DPRK will conduct a nuclear test, the report said, as plugging tunnels was the final step taken during its two previous nuclear tests.

Associated Press in Seoul