North Korea has fired what could be another ballistic missile in the fourth launch this year amid soaring tensions in the region.
An unidentified projectile was fired into the sea off North Korea's east coast on Monday, South Korea's military said.
Japan's coast guard has also confirmed that North Korea had launched what could be a ballistic missile.
The latest rocket launch comes after a series of missile strikes that were fired from the secretive state's coast into the sea since the start of the New Year.
Pyongyang is forging ahead with new military developments amid stalled stalks with the US and South Korea.
Since New Year's Day, North Korea has conducted three other tests, an unusual frequency of weapons tests.
Two of those launches involved single "hypersonic missiles" capable of high speeds and manoeuvring after launch.
The last, on Friday, involved a pair of short-range ballistic missiles (SRBMs) fired from train cars.
It was not immediately known what kind of missile was involved in Monday's launch.
The series of launches prompted U.S. President Joe Biden's administration to impose its first sanctions against Pyongyang on Wednesday, and to call on the U.N. Security Council to blacklist several North Korean individuals and entities.
North Korea has defended the missile tests as its sovereign right to self-defence and accused the United States of intentionally escalating the situation with new sanctions.
In a statement on the KCNA state news agency after the third rocket launch it said earlier that the country's recent development of a "new-type weapon" was just part of its efforts to modernise its national defence capability.
It added they had not targeted any specific country or harmed the security of neighbouring countries.
The statement warned of an unspecified "stronger and certain reaction" if the United States adopts a confrontational stance.
