The Japanese government said a projectile launched by North Korea on Tuesday might have been a ballistic missile, which goes against UN resolutions on Kim Jong-un’s regime.
Kyodo News reported the Japanese Defence Ministry’s initial conclusion, after earlier reports quoting South Korea’s Joint Chiefs of Staff that the North fired a projectile into waters off its east coast.
The launch comes after a test this month of two short-range ballistic missiles launched from a train.
That was North Korea’s first test of ballistic missiles since March, and followed what Pyongyang said was a trial of new, long-range cruise missiles a few days earlier.
North Korea, which is barred by UN resolutions from ballistic missile testing, has been building towards the ability to strike the US mainland with nuclear warheads and for tactical attacks against South Korea and Japan, which host tens of thousands of American troops.
Reports of the launch came as North Korea’s UN envoy, Kim Song, spoke to the annual UN General Assembly in New York.
"Nobody can deny the right to self-defence for the DPRK to develop, test, manufacture and possess the weapon systems equivalent to the ones which are possessed or being developed by them," Mr Kim said, referring to South Korea and the US policy towards Pyongyang.
"We are just building up our national defence in order to defend ourselves and reliably safeguard the security and peace of the country."
North Korea has already carried out several missile tests this month, one involving a long-range cruise missile and another with short-range ballistic missiles, the South's military said.
Seoul recently successfully test-fired a submarine-launched ballistic missile for the first time, making it one of a handful of nations with the advanced technology.
Mr Kim said annual joint military exercises between the US and South Korea, and "the deployment of all kinds of strategic weapons" towards the North, should be stopped "permanently."
The launch early on Tuesday in the Korean Peninsula came as the North was due to open a session of its rubber-stamp parliament, the Supreme People's Assembly.