Japan has called the launch a "clear violation of UN Security Council resolutions"
North Korea has fired what appears to be a short-range Scud missile off its east coast, South Korea's military has said.
The missile was launched from around the eastern North Korean coastal town of Wonsan, the South's Joint Chiefs of Staff said in a statement.
It flew about 280 miles (450 km) before landing in the sea in Japan's exclusive maritime economic zone.
There were no immediate reports of damage to planes or vessels in the area.
Japan's chief cabinet secretary Yoshihide Suga said the launch was "a clear violation of United Nations Security Council resolutions."
"Japan absolutely cannot tolerate North Korea's repeated provocative actions,” he said. “We have strongly protested to North Korea and condemn its actions in the strongest terms."
The White House said President Donald Trump has been briefed about the launch.
There was no immediate comment from the North's state controlled media.
Earlier on Sunday, North Korea tested a new anti-aircraft weapon system that Kim Jong Un says will "completely spoil the enemy's dream to command the air."
Pyongyang said glitches detected in an earlier test have been "perfectly overcome," paving the way for the weapon to be mass produced and deployed nationwide.
State media says the system is designed to "detect and strike different targets flying from any location" - and footage showed the drill taking place.
The North Korean leader said the system's hitting accuracy had improved since it was first tested in April 2016 and it would stop hostile nations "boasting of air supremacy and weapon almighty."
Three top officials accompanied the leader for the launch - including a veteran rocket scientist, a former air force general and the head of the blacklisted agency which is believed to be developing North Korea's missiles and nuclear weapons.
Last Monday, the secretive state said it had successfully tested an intermediate-range ballistic missile that met all technical requirements and could also be mass produced, but experts have questioned the extent of the country's progress.
A day later, the head of the US Defence Intelligence Agency said North Korea is on an "inevitable" path to obtaining a nuclear-armed missile capable of striking America if action is not taken.
However, Western experts believe Pyongyang is a few years away from successfully developing such a weapon.
North Korea's defiant ballistic missile tests have created tensions with Washington in recent months.
The reclusive nation has continued with its programme despite painful UN and unilateral sanctions - and described such punishment as an infringement of its right to self-defence.
Pyongyang maintains nuclear weapons are necessary to counter US aggression, but America denies it has any intention to attack.