All eyes are on North Korea to see if it marks the birthday of late founder Kim Il-sung on Monday with a missile launch, despite tension-reducing noises from Seoul and Washington.

North Korea has a habit of linking high-profile military tests with key dates in its annual calendar. The centenary of Kim's birth last year was preceded by a long-range rocket test that ended in failure.

South Korean intelligence says the North has had two medium-range missiles primed and ready to fire for nearly a week, with many observers tapping Monday's anniversary as a likely launch date.

US Secretary of State John Kerry, currently in Japan on the last leg of a whirlwind North-East Asia tour, warned North Korea when he was in Seoul on Friday that a launch in the current climate would be a "huge mistake".

The Korean peninsula has been in a state of heightened military tension since the North carried out its third nuclear test in February.