Donald Trump has said North Korea is "looking for trouble" and warned the US would "solve the problem" - with or without China's help.
The President's defiant Twitter message came after Pyongyang promised a strong response if the US "dares opt for a military action", warning such a move would have "catastrophic consequences".
Washington has sent the USS Carl Vinson aircraft carrier and its battle group to the region for annual US-South Korea war games, which Pyongyang views as a dress rehearsal for an invasion.
The US says it is aimed at maintaining "readiness and presence" in the region.
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Tensions on the Korean peninsula are already high because of recent ballistic missile launches by the North, which violate UN resolutions.
Russia's foreign ministry said in a statement it was "really worried" about what the US "has in mind for North Korea", ahead of a visit to Moscow by US Secretary of State Rex Tillerson.
At the weekend Mr Tillerson said missile strikes on a Syrian air base in retaliation for a chemical weapon attack should serve as a warning for any country operating outside of international norms.
In the aftermath of that thinly veiled threat, a spokesman for North Korea's foreign ministry said: "We will hold the US wholly accountable for the catastrophic consequences to be entailed by its outrageous actions."
He added: "If the US dares opt for a military action, crying out for 'pre-emptive attack' and 'removal of the headquarters', the DPRK (the formal name for North Korea) is ready to react to any mode of war desired by the US."
Pyongyang has long maintained the US is preparing some kind of assault against it and justifies its pursuit of nuclear weapons as defensive in nature.
A top US official said on Sunday that President Trump had asked his advisers for a range of options to rein in North Korea.
Mr Trump has previously threatened unilateral action against Pyongyang if China - the North's major ally - fails to help curb its neighbour's nuclear weapons programme.
But the North's latest response suggests the reclusive state is determined to continue on its current path, despite numerous rounds of UN sanctions.
North Korean leader Kim Jong-Un wants to develop a long-range missile capable of hitting the US mainland with a nuclear warhead.
Five nuclear tests have been staged so far, two of them last year, and there is speculation another test could be imminent.
The North is set to mark the 105th birthday of its late founding leader on Saturday, an occasion sometimes celebrated with a display of military might.
South Korea's prime minister and acting president has also warned of a "grave provocation" by Pyongyang to coincide with other anniversaries, including the 25 April foundation day for its army.