Seoul's Joint Chiefs of Staff said: "North Korea fired an unidentified projectile into the East Sea," referring to the Sea of Japan.

The Japanese coastguard also confirmed the launch.

"North Korea appears to have launched a possible ballistic missile," a Coast Guard spokesman told AFP without giving details on a possible trajectory.

The launch would be Pyongyang's fourth weapons test so far this year.

On Friday, North Korea fired two railway-borne tactical guided missiles. It also said it had tested hypersonic missiles on January 5 and January 11.

In response to the string of launches, the United States last week imposed new sanctions on the nuclear-armed country -- which Pyongyang said was a "provocation".

North Korea has a "legitimate right" to self-defence, a foreign ministry spokesman told KCNA.

Despite biting international sanctions over its weapons programs, Pyongyang has doubled down on its drive to modernise the military, while refusing to respond to US appeals for talks.

At a key meeting of North Korea's ruling party last month, Kim vowed to continue building up the country's defence capabilities.

Dialogue between Washington and Pyongyang remains stalled, and impoverished North Korea is also under a rigid self-imposed coronavirus blockade that has hammered its economy.