North Korea fired two suspected short-range ballistic missiles at sea Saturday morning, according to South Korea's military.
The launch is the seventh since North Korea completed a 1
Pyongyang has repeatedly expressed anger at US-South Korean military-US exercises.
On Saturday, South Korea said that the latest rockets fired after the exercise ended are of "grave concern".
Military officials said the shells were fired at 06:45 and 07:02 local time (21:45 and 22:02 GMT on Friday) from the eastern city of Sondok in South Hamong province.
They said they had flown about 380 km (240 miles) and reached 97 km altitude before landing in the Sea of Japan, also known as the East Sea.
"Our army is monitoring the situation in the event of additional launches and maintaining readiness," the Joint Chief of Staff of South Korea (JCS) said in a statement.
Japan's Defense Minister Takeshi Ivey confirmed that the missiles had not landed in Japanese territorial waters, but described them as a clear violation of UN resolutions.
The rocket launch comes days after the end of military exercises between the US and South Korea. North Korea describes them as a "rehearsal for war" and says they violate agreements reached with US President Donald Trump and South Korean President Moon Jin.
The United States and South Korea have refused to abolish the teachings but have scaled them.
In a statement issued by the Presidential Office on Saturday, South Korea called on North Korea to halt military escalation and reiterated its desire to resume negotiations with the United States.
The denuclearization talks were delayed by the second summit between Mr Trump and North Korean leader Kim Jong Un in February.
In June, the two leaders met in the Demilitarized Zone (DMZ) between two Koreas and agreed to resume negotiations at the working level.
Speaking after the tests on Saturday, Mr Trump reiterated that he had "really good relations" with Mr Kim, whom he said was "quite right" with him.