State media in Pyongyang said the Yongbyon complex is back in operation and that the country is ready to launch nuclear weapons "at any time."
Seoul has said the man — presumed to be a serviceman — walked across one of the world's most heavily militarized borders — the first time someone has done so since 2012.
The North Korean leader has been photographed smiling, having apparently climbed to the top of Mt. Paektu, the country's state-run news agency said.
CNN spoke to Kenneth Bae, Matthew Todd Miller and Jeffrey Edward Fowle at a hotel in Pyongyang
As North Korea bars a State Department envoy, Bae's options look slim.
“I’m sure the Iranians are paying close attention to our failure to prevent the North Koreans from continuing successful nuclear program,” John McCain says. Foreign policy hands aren't buying it.