North Korea fired two ballistic missiles into the sea off its east coast, South Korea said on Wednesday.
The latest launches came as North Korean leader Kim Jong Un is in Russia for talks with President Vladimir Putin.
South Korea’s military said it detected two short-range ballistic missiles launched from the Sunan area into the East Sea around 11:43 to 11:53 on Wednesday morning.
“Our military will closely monitor North Korea's activities in preparation for further provocations, in close cooperation with the United States, while maintaining a firm readiness posture based on the ability to respond overwhelmingly to any provocation,” said South Korea’s National Security Council.
The council added that North Korea's repeated missile launches are "a significant provocation that harms peace and prosperity" on the Korean peninsula and in the international community.
Wednesday’s launches were the first to occur while Kim was on a rare trip abroad.
They are the latest in a series of missile tests and military exercises conducted by North Korea in recent weeks. Pyongyang launched several cruise missiles toward the Yellow Sea on September 2, following its firing of a pair of short-range ballistic missiles from the Sunan area toward waters east of the peninsula on August 30.
In Tokyo, Japan's Chief Cabinet Secretary, Hirokazu Matsuno, told reporters at a news conference that Japan had lodged a formal protest with North Korea through Japan's embassy in Beijing.
Japan’s Prime Minister Fumio Kishida also instructed related ministries to gather information and ensure the safety of aircraft and ships.
United Nations Security Council resolutions ban all North Korea's ballistic missile and nuclear weapons activities. Officials in Seoul and in Tokyo said they strongly condemn Pyongyang’s missile launches and urged North Korea to stop them immediately.
Lee Juhyun contributed to this report.