In an exchange of threats, President Donald Trump has warned Pyongyang of "fire and fury like the world has never seen" and the North's military has claimed it was examining plans for attacking the U.S. territory of Guam.

North Korea threatens Guam regularly, but also knows a pre-emptive attack on U.S. citizens would assure annihilation of its own revered leadership Pyongyang's mid-range missiles also haven't been tested enough to be certain of their reliability in a real attack on a distant target.

Even so, the competing threats and Trump's use of North Korea-style rhetoric — Pyongyang has long vowed to reduce Seoul to a "sea of fire" — raise already high animosity and heighten worries that a miscalculation might spark conflict between the rivals.