North Korea fired two suspected short-range ballistic missiles into the sea on Saturday morning, South Korea's military says.
The launch is the seventh carried out since North Korea ended a 17-month hiatus on testing at the end of July.
The launch was supervised by North Korean leader Kim Jong-un, the state news agency KCNA later reported.
The agency said it was a test of a "super-large multiple rocket launcher", which it said was "newly-developed".
Kim Jong-un called the device a "great weapon," evincing "high appreciation" for the team which had developed and built it, KCNA said.
Military officials said the projectiles were launched at 06:45 and 07:02 local time (21:45 and 22:02 GMT Friday) from the eastern town of Sondok in South Hamgyong Province.
They said they flew about 380km (240 miles) and reached an altitude of 97 km before landing into the Sea of Japan, also known as the East Sea.
"Our military is monitoring the situation in case of additional launches and maintaining a readiness posture," South Korea's Joint Chiefs of Staff (JCS) said in a statement.
Japan's Defence Minister, Takeshi Iwaya, confirmed the missiles had not landed in Japanese territorial waters, but described them as a clear violation of UN resolutions.
Pyongyang has repeatedly expressed anger at US-South Korean military exercises that have been taking place.
The missile launch comes days after US-South Korean military exercises ended. North Korea describes them as a "rehearsal for war" and say they violate agreements reached with US President Donald Trump and South Korea's President Moon Jae-in.
The US and South Korea have refused to cancel the drills, but have scaled them back significantly.
In a presidential office statement on Saturday, South Korea called for North Korea to stop escalating military tensions and reiterated their wish for negotiations with the US to resume.
Denuclearisation talks have stalled since a second face-to-face summit between Mr Trump and North Korean leader Kim Jong Un broke down in February.
In June the two leaders met in in the Demilitarized Zone (DMZ) between the two Koreas and agreed to resume working-level negotiations.
Speaking after Saturday's tests, Mr Trump reiterated that he had a "really good relationship" with Mr Kim, whom he said had been "pretty straight" with him.