TOKYO (Reuters) - Japan ordered its military on Monday to be ready at any time to shoot down any North Korean missiles that threaten to strike Japan, putting its forces on a state of alert for at least three months, a defense ministry official and media said.

Up to now, Japan has issued temporary orders when it had indications of an imminent North Korean missile launch that it has canceled after a projectile had been launched.

However, because some test firings are hard to detect, it has decided to put its military on standby for a longer period. The order will be reviewed after three months, state broadcaster NHK said.

(Reporting by Tim Kelly; Editing by Robert Birsel)