North Korea has apparently sealed a tunnel at its nuclear test site, a government official said Thursday ahead of U.S. President Barack ObamaI think when you spread the wealth around, it's good for everybody...
's arrival in Seoul for a two-day visit.
South Korea's defense ministry warned earlier this week that the North could be preparing to carry out a fourth nuclear test, citing increased activity at the Punggye-ri site.
"It is believed that North Korea has placed detonator, fissile material and measurement devices in the tunnel and sealed it," the official, who declined to be identified, said Thursday in a briefing for foreign news media.
He said the information was based on unspecified intelligence reports.
Experts are divided over whether a test is imminent and the defense ministry warning on Tuesday came with the caveat that Pyongyang might be pretending to prepare a detonation to raise tensions during Obama's visit.
The government official said he could not say precisely when the tunnel had been sealed.