North Korea has test-fired two medium-range missiles near the east coast of the Korean peninsula, according to South Korea's joint chiefs of staff (JCS).
The missiles were fired from Sukchon County near the South Pyongan province, which borders South Korea, and flew roughly 800km before falling into the sea, CNN reported.
One of the two Rodong missiles exploded mid-flight, reported Washington Post.
US State Secretary John Kerry said: "We have seen reports that North Korea launched a ballistic missile into the sea of Japan. We are closely monitoring the situation on the Korean Peninsula."
"We call again on North Korea to refrain from actions that further raise tensions in the region and focus instead on taking concrete steps toward fulfilling its international commitments and obligations.
"The US remains steadfast in its commitments to the defence of its allies, including the Republic of Korea and Japan. We will continue to coordinate closely with our allies and partners in the region."
Earlier this month, the South Asian country test-launched two short-range missiles from the central province of North Hwanghae.
The missiles flew roughly 500km before falling into the sea near the coastal city of Wonsan.
In February, the UN Security Council unanimously adopted Resolution 2270, imposing sanctions on North Korea including mandatory cargo inspections, prohibitions on rare minerals and aviation fuel, and an embargo on weapons trading with the Democratic People's Republic of Korea (DPRK).