Seoul: North Korea on Wednesday test-fired a submarine-launched ballistic missile (SLBM) in waters off its east coast, the South Korean military said. The launch near the port city of Sinpo around 5.30 a.m. (local time) was in an apparent show of defiance against the ongoing military drill between Seoul and Washington, Yonhap news agency quoted Joint Chiefs of Staff (JCS) as saying. The military said the missile flew about 500 km, which is an improvement compared with past launches. It fell into waters inside Japan's air defence identification zone. Tensions are high on the divided peninsula as North Korea threatened on Monday to wage a "pre-emptive nuclear strike" on South Korea and the US against the allies' annual military exercise.