Tokyo and Seoul's governments both said that North Korea had launched what could be a ballistic missile towards waters off its eastern coast. It follows two days of bellicose rhetoric aimed at the US from Pyongyang.
Japanese and South Korean officials reported a potential ballistic missile launch from North Korea on Wednesday morning.
"North Korea fired an unidentified ballistic missile into the East Sea," South Korea's Joint Chiefs of Staff said, referring to the body of water also known as the Sea of Japan.
Japan's Coast Guard and Defense Ministry made similar statements.
The developments follow two days of critical comments from North Korea aimed at the US, complaining of supposed US aerial reconnaissance flights over its territory. The reclusive regime's leader Kim Jong Un's influential sister Kim Yo Jong had also spoken about the issue, threatening reprisals.
It also coincides with NATO's leaders summit in Vilnius, Lithuania, which South Korean President Yoon Suk-yeol is attending.
North Korea also recently tried and failed to launch a spy satellite, whose wreckage Seoul has been analyzing.
International sanctions prohibit Pyongyang from testing ballistic missiles and launching satellites, but it has been flouting such restrictions for years, and with increased regularity more recently.
