North Korea has said it will go to war if US President Donald Trump provokes them.
The country said it is prepared to use its most "powerful nuclear deterrent" if the US "comes with reckless military manoeuvres".
Vice foreign minister Han Song Ryol told the Associated Press: "We've got a powerful nuclear deterrent already in our hands, and we certainly will not keep our arms crossed in the face of a US pre-emptive strike."
Mr Han has accused Mr Trump of "making trouble" with "aggressive" tweets.
He cited not only the US-South Korean wargames and the deployment of the aircraft carrier, the USS Carl Vinson, but also a tweet Mr Trump posted on Tuesday in which he said the North is "looking for trouble".
The president also tweeted that if China does not do its part to rein in Pyongyang's nuclear ambitions, the US can handle it.
Tensions are deepening after the US sent a Navy strike group to waters off the peninsula and President Trump warned he is willing to "deal with North Korea".
America and its allies have expressed alarm about North Korea's recent ballistic missile tests, and the US has been conducting war games with South Korea.
There is speculation North Korean leader Kim Jong Un might conduct a missile test to mark the 105th anniversary of the birth of the state's founder, Kim Il Sung, on Sunday.
NBC News reported the US is prepared to launch a pre-emptive strike with conventional weapons against the North if officials believe it is poised to carry out a nuclear test.
Washington's primary concern is the North developing the ability to mount a nuclear warhead on an intercontinental missile.
Mr Trump has tried to persuade Chinese President Xi to put pressure on its ally North Korea to stop its nuclear programme.
US-based monitoring group 38 North said satellite imaging appears to show the country's nuclear site is "prime and ready" for a new test.
It claimed the pictures revealed "new activity" in the site's administration area plus what appeared to be piles of equipment covered in tarpaulins or nets.
North Korea launched a long-range rocket carrying a satellite on April 13, 2012, to mark the centenary of Kim Il Sung's birth.