North Korea threatened Thursday to "take merciless retaliatory counteraction" against the United States, after the Pacific deployment of American aircraft capable of launching nuclear attacks.
The U.S. Strategic Command said earlier this week that three B-2 Spirit bombers had temporarily been stationed at Andersen Air Force Base on Guam.
Pyongyang's warning -- carried by its state-run KCNA news agency -- cautioned that "a pre-emptive nuclear attack is not a monopoly of the United States."
The North is growing wary ahead of the upcoming Ulchi-Freedom Guardian, a joint military exercise starting Aug. 22 that will involve the U.S. and South Korea, where nearly 30,000 American troops are based in any case.
A recent debate in the U.S. has centered on whether the Barack Obama administration may leave a pacifist legacy before a successor is elected in November's presidential election -- one option could see Washington adopt a so-called "no first use" policy regarding nuclear weapons.
Nevertheless, North Korea accused the country of having "already examined at the phase of an actual war the capabilities of nuclear strategic bombers for mounting the pre-emptive nuclear attack."
The reclusive North has already been honing its own ability to strike Guam among other targets with a series of medium-range ballistic missile tests this year, despite being lumbered with strengthened United Nations sanctions following its fourth ever nuclear test in January.
Military drills south of the inter-Korean border often stir up further provocations by Pyongyang, as it sees such exercises as preparations for an invasion.
The Koreas have held an uneasy truce since the close of the 1950-53 Korean War, during which the U.S. fought on the South's side.