South Korea had earlier detected signs that North Korea was preparing to launch a submarine-launched ballistic missile, the president’s office said Saturday, which Pyongyang last tested in May. Today’s launch is the latest in a series of Pyongyang’s most intense nuclear tests ever, including the launch of a long-range ICBM.

The Japanese Coast Guard also confirmed the possible launch of ballistic missiles, citing information from the Tokyo Defense Ministry. Ships in the area were asked to watch for unidentified objects and provide information. Japanese public broadcaster NHK said the object appeared to have fallen outside Japan’s exclusive economic zone.