North Korea has nothing to fear from any US move to broaden sanctions aimed at cutting it off from the global financial system and will pursue "acceleration" of its nuclear and missile programmes, a North Korean envoy told Reuters on Tuesday.

This includes developing a "pre-emptive first strike capability" and an inter-continental ballistic missile (ICBM), said Choe Myong Nam, deputy ambassador at the North Korean mission to the United Nations in Geneva.

Reuters, quoting a senior U.S. official in Washington, reported on Monday that the Trump administration is considering sweeping sanctions as part of a broad review of measures to counter North Korea's nuclear and missile threat.

"I think this is stemming from the visit by the Secretary of State (Rex Tillerson) to Japan, South Korea and China...We of course are not afraid of any act like that," Choe told Reuters.

"Even prohibition of the international transactions system, the global financial system, this kind of thing is part of their system that will not frighten us or make any difference."

He called existing sanctions "heinous and inhumane".

North Korea has been under sanctions for "half a century" but the communist state survives by placing an emphasis on juche or "self-sufficiency", he said. His country wants a forum set up to examine the "legality and legitimacy of the sanctions regime".

He denounced joint annual military exercises currently being carried out by the United States and South Korea on the divided peninsula and criticised remarks by Tillerson during his talks with regional allies last week.

"All he was talking about is for the United States to take military actions on DPRK," Choe said, using the acronym for the Democratic People's Republic of Korea.

North Korea rejects claims by Washington and Seoul that the military drills are defensive. They involve strategic nuclear bombers and a nuclear submarine, Columbus, that recently entered South Korean ports, he said.

"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."


PRE-EMPTIVE STRIKE CAPABILITY

"We strengthen our national defence capability as well as pre-emptive strike capabilities with nuclear forces as a centrepiece," Choe said.

Asked to comment on Choe's remarks, a U.S. State Department spokeswoman, Anna Richey-Allen, called on North Korea "to refrain from provocative actions and inflammatory rhetoric...and to make the strategic choice to fulfil its international obligations and commitments and return to serious talks.”

Choe declined to give technical details of North Korea's latest rocket engine test on Sunday - seen as a possible prelude to a partial ICBM flight - calling it a great historical event that would lead to "fruitful outcomes".

"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," Choe said, recalling leader Kim Jong Un's pledge in a New Year's address.

Analysts say North Korea has likely mastered the technology to power the different stages of an ICBM and may show it off soon, but is likely still a long way from being able to hit the mainland United States.

"The United States has been talking about launching pre-emptive strikes at North Korea," Choe said. "And we have been prepared to deter, to counter-attack such attacks on the part of the United States.

"We would utilise every possible means in our hands and the inter-continental ballistic rocket is one of them."