SEOUL, South Korea (AP) — North Korea fired two ballistic missiles into the sea off its east coast Monday night, the South Korean military said, hours after a US nuclear-powered submarine arrived at a naval base in the South.

Japan’s Defense Ministry also reported the launch of what it said were two ballistic missiles by North Korea, which landed outside its exclusive economic zone.

The launches come amid heightened tensions on the Korean peninsula, as South Korea and the United States take steps to increase their military readiness against North Korea’s weapons program by deploying strategic US military assets.

North Korea has reacted angrily, saying such a deployment could meet the criteria for the use of nuclear weapons.

The United States said it was consulting closely with allies about North Korea’s missile launches, which it described as destabilizing.

In a statement on Monday, the US military added that the launches did not pose an immediate threat to US personnel and territory or to US allies.

Earlier on Monday, a US nuclear-powered submarine entered a naval base on the southern South Korean island of Jeju to load military supplies while on an unspecified operational mission, the South Korean navy said.

Over the weekend, North Korea fired a barrage of cruise missiles into the sea off its west coast.

Last week, North Korea conducted ballistic missile tests after a nuclear-armed US submarine pulled into a South Korean port for the first time since the 1980s.