It comes after the country released a propaganda video purporting to show a US aircraft carrier on fire
North Korea will pursue the development of inter-continental ballistic missiles and first strike capability, an envoy has said.
The Pyongyang official said his country has nothing to fear from any threats by the US that it will broaden sanctions.
Instead, Choe Myong-Nam warned, North Korea will accelerate its nuclear and missile programme.
It comes after the country released a propaganda video purporting to show a US aircraft carrier on fire.
Mr Choe, deputy ambassador at the DPRK (North Korean) mission to the United Nations in Geneva, told Reuters his country would work towards developing the sort of nuclear capability that allowed it to strike at an enemy first.
It would also aim to build a long-range missile that had the potential to hit targets on other continents.
In the last few weeks, the US has held joint military exercises with South Korea which America says are defensive.
President Trump said soon after taking office that he would not let North Korea possess a weapon that could threaten the US.
A senior US official in Washington said on Monday that the Trump administration is considering sweeping sanctions as part of measures to counter North Korea's nuclear and missile threat.
But Mr Choe said: "We of course are not afraid of any act like that.
"In the light of such huge military forces involved in the joint military exercises, we have no other choice but to continue with our full acceleration of the nuclear programmes and missile programmes.
"It is because of these hostile activities on the part of the United States and South Korea."
"We strengthen our national defence capability as well as pre-emptive strike capabilities with nuclear forces as a centrepiece," Mr Choe added.
He went on to state that it was up to North Korea when and where it tests the missiles it builds.
"I can tell you for sure that the inter-continental ballistic rockets of the DPRK will be launched at any time and at any place as decided by our Supreme Leadership," he said.
On Monday, US Secretary of State Rex Tillerson met Chinese President Xi Jinping - who he hopes will help to curb North Korea's nuclear weapons programme.
As he did so, North Korean state media said Supreme Leader Kim Jong-Un attended the test of a new high-thrust engine to propel rockets at the Sohae launch site.
Additional reporting from IRN