Following a rapid diplomatic rapprochement this year, the North's leader Kim Jong Un and President Donald Trump signed a vaguely-worded statement in Singapore in June, agreeing to work towards the "denuclearisation of the Korean peninsula".

But the two countries have since disagreed on what it means, causing follow-up negotiations to stall.

Now Pyongyang is demanding sanctions relief and has condemned US insistence on its nuclear disarmament as "gangster-like", while Washington is pushing to maintain the measures against the North until its "final, fully verified denuclearisation".

Thursday's commentary released by the North's official Korean Central News Agency (KCNA) asserted that the commitment was a mutual rather than unilateral undertaking.

"It must be clearly understood that the denuclearisation of the Korean peninsula means the removal of all nuclear threats -- not only those from the North and the South but those aiming at the Korean peninsula from surrounding areas as well", it said.

It urged the US to give up the "delusion" of forcing the North to give up its nuclear arsenal "unilaterally" through "pressure and coercion".

It also called for the lifting of sanctions, describing it as a "touchstone" in determining whether the US was committed to implementing the Singapore agreement.

A second summit between Trump and Kim -- who exchanged personal insults and threats of war throughout 2017 -- is expected to take place next year.

The US leader faces criticism over the planned talks since North Korea has taken few concrete steps to abandon its nuclear and ballistic missile programmes.

Pyongyang has long said it needs the weapons to deter a possible US invasion.

It has spent decades developing them, at a heavy cost in both resources and the imposition of multiple sets of UN, US, EU and other sanctions.

Washington last week added three senior North Korean officials to those subject to sanctions over human rights abuses, including Choe Ryong Hae, who has been considered a right-hand man to Kim.

Pyongyang condemned the move, warning Washington's approach could "block the path to denuclearisation on the Korean peninsula forever".

Trump played down hopes last week for any imminent deal to persuade Pyongyang to give up its nuclear arsenal but he also expressed optimism, saying North Korea's economy has "wonderful potential" and that Kim "sees it better than anyone and will fully take advantage of it for his people".