The US is waiting for Pyongyang to account for all its nuclear activities
North Korea has pledged to strengthen its "war deterrent", days after it missed a year-end deadline for declaring its nuclear activities.
The move was a response to US military modernisation and aggression, party daily Rodong Sinmun said.
North Korea has made similar statements before, and the remarks often coincide with differences over the ongoing nuclear disarmament process.
Under a 2007 deal, Pyongyang pledged to go nuclear-free in exchange for aid.
It has already begun the process of disabling its Yongbyon nuclear reactor.
But it failed to produce a full declaration of all its nuclear activities by year-end - and as yet has not explained why.
"Our republic will continue to harden its war deterrent further in response to the US stepping up its nuclear war moves," the daily newspaper said.
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The phrase "war deterrent" is seen by many as a reference to Pyongyang's nuclear arsenal.
A second state daily, Minju Joson, linked delays in the disablement process at Yongbyon to slow provision of international aid, echoing comments by an official last week.
"It is fully up to the US and related countries whether the goal of denuclearising the Korean peninsula would be attained or not," the daily said.
Yongbyon was due to be disabled by the end of this year, but there has been a delay, reportedly due to technical reasons.
However, it is the lack of a written declaration providing a complete account of all Pyongyang's nuclear activities that is of more concern to the international community.
In particular, the US wants to know how much plutonium has been produced by North Korea, and also see evidence that there is no secret programme for uranium enrichment for weapons purposes.
On Monday, a Chinese spokesman played down concern over the missed deadline, but a US official recently expressed scepticism that a declaration would ever be forthcoming.
US envoy Christopher Hill is due back in the region on Monday in a bid to move negotiations forward.