South Korean and U.S. intelligence agencies have detected signs that North Korea is preparing for a fourth nuclear test.
"There has been a very brisk movement of vehicles and people in and around the Punggye-ri nuclear test site," a government source here said on Monday. "We're keeping a close watch on their movements."
"It doesn't look like the North is going to conduct a nuclear test in a day or two, but I don't think it's physically impossible for the North, if it has the political will, to do it to coincide" with U.S. President Barack Obama's visit to South Korea on Friday and Saturday, another source said.
Friday is also the North Korean Army's founding anniversary, which is another reason why that would be an opportune date.
The North conducted its third nuclear test in the western tunnel of the Punggye-ri test site in February last year. Currently, the southern tunnel looks ready for a test after a few more days of work.