North Korea fired two ballistic missiles into the sea off its east coast late on Monday, South Korea's military said, hours after a US nuclear-powered submarine arrived in a naval base in the South.
Japan's defense ministry also reported the launch of what it said could be a ballistic missile by North Korea. Japanese media said there may have been multiple missiles launched, citing a Japanese government source.
The reports come amid heightened tensions on the Korean peninsula as South Korea and the United States take steps to boost military readiness against North Korea's weapons program with the deployment of US strategic military assets.
North Korea has reacted angrily, saying such deployment could meet the criteria for its use of nuclear weapons.
US submarine entered South Korean naval base
Earlier on Monday, a nuclear-powered US submarine entered a naval base in South Korea's southern island of Jeju, to load military supplies while on an unspecified operational mission, the South Korean navy said.
Over the weekend, the North fired a barrage of cruise missiles into the sea off its west coast.
Last week, North Korea conducted ballistic missile tests, that time after a nuclear-armed US submarine arrived at a South Korean port for the first time since the 1980s.