The communist country's state media has said its strategic rocket and long-range artillery units have been ordered to enter the highest level of combat mode and are trained on three targets.
Kim Jong-Un's dictatorship said on television it would be looking to hit Guam, Hawaii and mainland America after U.S. bombers flew more sorties threatening the North.
Observations: North Korea has threatened to fire missiles at America as it stepped up its military exercises as leader Kim Jong-Un tries to show military strength
'From this moment, the Supreme Command of the Korean People's Army will be putting in combat duty posture No. 1 all field artillery units including long-range artillery units strategic rocket units that will target all enemy object in U.S. invasionary bases on its mainland, Hawaii and Guam,' the North's KCNA news agency said.
South Korea's defence ministry said it had detected no signs of unusual activity by the North's military but will monitor the situation. The South and the U.S. military are conducting drills until the end of April, which they have stressed are strictly defensive in nature.
But the rival Koreas have had several bloody naval skirmishes in disputed Yellow Sea waters and there is some worry among experts in the region that more fighting could follow.
The North previously threatened nuclear attack on the United States and South Korea, although it is not believed to have the technology to hit continental United States with an atomic weapon.
It has responded angrily to reports that America has flown B-52 bomber sorties over the Korean peninsula as part of the annual military drills with South Korean forces.
Test: North Korea has also threatened to launch precision attack weapons at US Navy bases in South East Asia. Here an anti-aircraft missile is fired during a drill in front of the country's leader Kim Jong-un
Threat: A large number U.S. military bases are within range of the new missiles - shown here
North Korea has stepped up its military exercises in response to what it regards as 'hostile' joint drills by South Korea and the United States after Pyongyang was sanctioned by the U.N. Security Council for a nuclear test in February.
It is not known if North Korea possesses drones, although a report on South Korea's Yonhap news agency last year said that it had obtained 1970s-era U.S. target drones from Syria to develop into attack drones.
Tensions have mounted on the Korean peninsula since North Korea staged its first successful long-range rocket launch in December. It followed this up with its third nuclear weapons test in February.
Aggressive: North Korea's supreme military command said it had U.S. bases in Guam and Okinawa in their sights. This picture shows a military drill of the Korean People's Army at an undisclosed location in North Korea.
Andersen Air Force Base, Guam: North Korea is objecting to the flights of B-52's (pictured) over the Korean peninsula - threatening massive retaliation
Pyongyang is barred from developing missile and nuclear-related technology under U.N. sanctions imposed after previous nuclear tests.
Most military experts say that the North will likely not launch an all-out war against South Korea and its U.S. ally due to its outdated weaponry.
Pyongyang is viewed as more likely to stage an attack along a disputed sea border between the two countries as it did in 2010 when it shelled a South Korean island, killing four people.
Such a move would provide a major test for new South Korean President Park Geun-hye, who took office pledging closer ties with the North if it abandoned its nuclear push.
Military: The threat to US bases from North Korean will be a cause for concern in Washington. Here North Korean tank troops take part in military drills
Force: The north's sabre rattling will also lead to increasing anxiety in neighbouring South Korea - which is a close ally of the US
