North Korea has threatened to attack American airbases on the Japanese island of Okinawa and the Pacific island of Guam.
A statement by Kim Yong Chul, the spokesman of the Supreme Command of the Korean People's Army warned of "military actions".
"The US should not forget that the Anderson Air Force Base on Guam where B-52 bombers take off and naval bases in Japan and Okinawa where nuclear-powered submarines are launched are within the striking range of the Democratic People's Republic of Korea (DPRK) precision strike means," the statement read.
"Now that the US started open nuclear blackmail and threat, the DPRK, too, will move to take corresponding military actions."
The words mark the latest escalation in a lengthy stand-off as North Korea defies calls from the rest of the world to halt its dual nuclear and ballistic missile programmes.
The American government has not yet responded to the threat.
British diplomatic sources speaking to Sky News from Seoul have said the UK Government "takes any threats seriously and there is some concern over the more harsh rhetoric coming from the DPRK".
However, the source insisted that there was no panic or alarm among diplomatic circles and that UK travel advice to South Korea remains unchanged.
The latest threat from North Korea is a direct response to a series of joint military exercises involving the US and South Korea.
On Tuesday, the US Air Force deployed its giant B-52 bombers from their base on Guam. The planes, which are capable of carrying and deploying nuclear bombs, flew sorties over the Korean peninsula as part of the military exercise.
The Pentagon in Washington confirmed the B-52 deployment. Spokesman George Little said the US wanted to underline its commitment and capacity to defend South Korea against an attack from the North.
However, the flights were condemned by Pyongyang as "an unpardonable provocation".
"The US is introducing a strategic nuclear strike means to the Korean peninsula at a time when its situation is inching close to the brink of war," the North Korean statement added.
The North Korean military does have rockets capable of reaching both Okinawa and Guam.
The surprisingly successful rocket launch in December followed a trajectory similar to that which any strike against Okinawa would take.
Okinawa is 600 miles due south of the Korean peninsula. Guam is further away, to the east of the Philippines.
While Pyongyang has proved it has the range capability, it is not clear whether or not their missiles are accurate enough to hit a specific target. And the country does not yet have the ability to carry out a nuclear strike at this range.
Earlier this month, the UN imposed the toughest sanctions yet on North Korea.
Kim Jong-Un reacted with anger, threatening to attack America, South Korea and Japan. The young and unpredictable leader toured military units calling for them to prepare for 'all out war'.
Meanwhile, Wednesday's unusually large cyberattack in South Korea, which brought down banks and broadcasters for one hour, has been traced to China.
Experts in Seoul claim the simultaneous attacks all bore the same IP address, which was traced to the Chinese mainland.
Many of North Korea's internet and computing operations are tied to China. There is no suggestion that the Chinese government had any involvement.