South Korea’s Defense Ministry said, however, that it had seen no signs of an imminent attack.

The order is the latest in a series of fiery statements from isolated, nuclear-armed North Korea since joint military drills by the United States and South Korea began on March 11. The North threatened the United States with “pre-emptive nuclear strikes” earlier this month.

North Korea is not believed to have the capability to hit the continental United States with an atomic weapon.

But the US military's bases in the Pacific area are in range of its medium-range missiles, Reuters reported.

Analysts believe a direct North Korean attack is extremely unlikely, especially during the drills, which conclude on April 30. But the rival Koreas have had several bloody naval skirmishes in disputed Yellow Sea waters and there's some concern among analysts about a provocation after the drills, Associated Press reported.

Tensions remain high on the Korean Peninsula in the aftermath of North Korea's third nuclear test on February 12. The test sparked harsh international condemnation and led to new UN sanctions against Pyongyang.