North Korea fired three short-range ballistic missiles toward its eastern waters in its latest weapons display on Saturday.
The missile launch came a day after rival South Korea conducted a rocket launch related to its push to build a space-based surveillance to better monitor the North.
Tensions between the two states rose this week when South Korea accused North Korea of flying five drones across the tense border for the first time in five years and responded by sending its own drones toward the North.
South Korea's Joint Chiefs of Staff said in a statement it detected the three launches from an inland area south of Pyongyang, the North's capital, on Saturday morning.
It said the three missiles travelled about 350 kilometers (220 miles) before landing in the waters between the Korean Peninsula and Japan. The estimated range suggests the missiles tested could target South Korea.
The Joint Chiefs of Staff called the launches "a grave provocation" that undermines international peace. It said South Korea maintains a readiness to "overwhelmingly" deter any provocation by North Korea.
The US Indo-Pacific Command said the launches highlight "the destabilizing impact" of North Korea's unlawful weapons programs and that the U.S. commitments to the defense of South Korea and Japan "remain ironclad."
Earlier Saturday, Japan's Defense Ministry also reported suspected ballistic missile launches from North Korea.
South Korea's military on Monday scrambled warplanes and helicopters, but they failed to shoot down any of the North Korean drones before they flew back home or vanished from South Korean radar.
One of the North Korean drones traveled as far as northern Seoul, triggering security jitters among many people in the South.
South Korea still flew three of its surveillance drones across the border on Monday in an unusual tit-for-tat. South Korea on Thursday staged large-scale military drills to simulate shooting down drones.
South Korean President Yoon Suk Yeol has called for boosting his country's air defense network and vowed to sternly deal with provocations by North Korea.
Since taking office in May, Yoon's government has expanded regular military drills with the U.S. in the face of increasing North Korean nuclear threats.
North Korea has called such drills an invasion rehearsal and argued its recent missile tests were its response.
But some experts say North Korea is using the South Korea-U.S. training as a pretext to modernize its arsenal and increase its leverage in future dealings with the U.S.
Before Saturday's launches, North Korea had already test-fired more than 70 missiles this year. Many of them were nuclear-capable weapons designed to attack the U.S. mainland and its allies South Korea and Japan.
Later Saturday, senior diplomats from South Korea, Japan and the United States jointly denounced the North's launches after a phone call.
They agreed to reinforce their deterrence against North Korea and work together to achieve the North's denuclearization, according to the South Korean and Japanese foreign ministries.
On Friday, South Korea test- launched a solid-fueled rocket, a type of a space launch vehicle that it plans to use to put its first spy satellite into orbit in coming years.
Defense officials said it was a follow-up test of the country's first successful launch of a solid-fuel rocket in March. The unannounced launch triggered a brief public scare of a UFO appearance or a North Korean missile.
