North's official Rodong Sinmun newspaper said: "Dark clouds of a nuclear war are hanging low over the Korean Peninsula."
"The ever-more frantic moves of the US to ignite a new war against (North Korea) would only compel it ... to bolster its deterrent for self-defence in every way," it said in a commentary carried by the state-run Korean Central News Agency on Saturday.
The North has repeatedly accused the US of planning to attack, but Washington has denied any such intention.
The North's comments on Saturday follow a South Korea-US agreement this month giving American troops more flexibility in the South.
The North said the pact was aimed at preparing for war.
Also on Saturday, the North dismissed US accusations of counterfeiting and other illicit activities like drug trafficking.
"The nature and mission of (North Korea) do not allow such things as bad treatment of the people, counterfeiting and drug trafficking to happen in it," KCNA said.
"Dark clouds of a nuclear war are hanging low over the Korean Peninsula"
North's official Rodong Sinmun newspaper
A pro-North Korean newspaper in Japan also urged Washington to prove its allegation that North Korea is counterfeiting US currency.
The Choson Sinbo newspaper said: "If there is suspicion and clear evidence as claimed by the United States, (the US) can present it and prove (it),"
The United States "continues to leak plausible information but the reality is that there is nothing to confirm the fact objectively," it said.