A US official confirmed America was assessing military options
North Korea will not "keep its arms crossed" in the face of a US pre-emptive strike, Pyongyang's vice foreign minister has said
Han Song Ryol told the Associated Press, Donald Trump was "making trouble" with "aggressive" tweets.
He added that North Korea will conduct its next nuclear test whenever supreme headquarters sees fit.
Mr Han spoke as a US official confirmed America was assessing military options in response to North Korea's weapons programmes.
"Military options are already being assessed," the official said.
Mr Han said the situation on the Korean Peninsula is now in a "vicious cycle".
Tensions are deepening as the US has sent an aircraft carrier to waters off the peninsula.
It is also conducting its biggest-ever joint military exercises with South Korea.
Pyongyang, meanwhile, recently launched a ballistic missile.
Some outside experts say it could conduct another nuclear test at virtually any time.
Many experts believe North Korea could have a viable nuclear warhead and a ballistic missile capable of hitting the US mainland within the next few years.
In comments reported by Reuters, Chinese Foreign Minister Wang Yi told reporters: "We call on all parties to refrain from provoking and threatening each other, whether in words or actions, and not let the situation get to an irreversible and unmanageable stage."
Mr Trump said in a tweet on Tuesday that the North is "looking for trouble".
US Vice President Mike Pence will travel to South Korea on Sunday in what his aides said was a sign of the US commitment to its ally.