North Korea has launched two ballistic missiles toward the Sea of Japan in Kim Jong-un's latest test.
The office of Japan's Prime Minister Fumio Kishida tweeted an "emergency alert" about the missile launch.
"North Korea has launched a suspected ballistic missile. More updates to follow," it said.
Approximately 30 minutes later, the Japanese Defense Ministry said North Korea had launched a second "possible ballistic missile".
South Korea's Joint Chief of Staff said the first launch was made on Sunday morning but gave no further details.
It comes just three days after North Korea said it tested a "high-thrust solid-fuel motor" for a new strategic weapon, a development that could allow it to possess a harder-to-detect arsenal of intercontinental ballistic missiles that can reach the US mainland.
In recent months, North Korea has test-fired a barrage of nuclear-capable ballistic missiles including last month's launch of its developmental, longest-range, liquid-fueled Hwasong-17 ICBM designed to carry multiple warheads.
Pyongyang has also conducted a series of short-range launches it described as simulated nuclear attacks on South Korean and US targets in an angry reaction to an expansion of joint US-South Korea military exercises that North Korea views as rehearsals for a potential invasion.
Some experts say North Korea would eventually use an expanded arsenal to seek sanctions relief and other concessions from the United States.