‘A huge explosion rocked North Korea three days ago but U.S. and South Korean officials said on Sunday it was unlikely to have been a nuclear weapons test despite a report the blast produced a mushroom cloud.
[..] in Washington, U.S. officials said there was no definitive explanation yet, although Thursday’s blast did not appear to be nuclear.’
‘North Korea is believed to be developing nuclear weapons. International experts would likely have been able to detect a test if one had occurred several days ago.
“We understand that a mushroom-shaped cloud about 3.5 to 4 kilometers (2.1 to 2.5 miles) in diameter was monitored during the explosion,” the source in Seoul told Yonhap.’