North Korea fired two ballistic missiles into the sea off its east coast late on Monday. South Korea's military said these missiles were fired hours after a U.S. nuclear-powered submarine arrived at a naval base in the South. Japan's defence ministry also reported the launch of what it said could be a ballistic missile by North Korea. 

The reports 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 programme with the deployment of U.S. strategic military assets. North Korea has reacted angrily, saying such a deployment could meet the criteria for its use of nuclear weapons.