Anchor: North Korea raised the possibility on Sunday of carrying out a new type of nuclear test. Since then, experts have been coming up with possible scenarios about how the North would pull it off, including the detonation of a nuclear device in the atmosphere. But the South Korean government says there are no imminent signs Pyongyang will carry out any such tests.
Our Kim So-yon reports.
 
Report: South Korea’s Defense Ministry said North Korea has dug a horizontal tunnel deep inside a mountain where a nuclear test could be held. 
 
But during a news briefing Tuesday, the ministry’s spokesman, Kim Min-seok, also made it clear there has been no indication the North plans to use the tunnel anytime soon. He said nothing suggests Pyongyang is moving equipment and devices for an actual test to the site.
 
The defense ministry's comments come after a U.S. arms control expert raised the possibility of an atmospheric nuclear test or an underground explosion in a vertical tunnel by North Korea. 
 
Jeffrey Lewis, the director of the East Asia Nonproliferation Program at the James Martin Center for Nonproliferation Studies, told Yonhap News Agency on Monday that North Korea could take a cue from China, which conducted an atmospheric nuclear test in 1966 with a nuclear warhead loaded on a missile.
 
Lewis also said North Korea might use a vertical tunnel instead of a horizontal tunnel to make an explosion more powerful.
 
Regarding an underground test, defense ministry spokesman Kim said a test in either tunnel would have the same effect. 
 
Kim also said North Korea could make a stronger statement of its nuclear power to neighboring countries by blowing up a device in the atmosphere. But he said this kind of test would be difficult because of the enormous international backlash Pyongyang would receive over the radioactive fallout.
Kim So-yon, KBS World Radio News.