The United Nations has strongly condemned North Korea's latest nuclear test and promised new measures against Pyongyang.
A North Korean ballistic missile fired from a submarine flew about 310 miles in the longest flight by that type of weapon, Seoul said - a range that can place much of South Korea within its striking distance.
North Korea fired three ballistic missiles into its eastern sea, after a week of verbal warnings over the South's decision to deploy an advanced US missile defence system, Seoul said.
North Korea is believed to have placed a new, powerful mid-range missile on standby for an impending launch, reports claim.
A North Korean launch of a missile on the birthday of its revered founder appears to have failed, US defence officials said.