North Korea issued a veiled threat to increase its nuclear arsenal if US officials do not quickly agree to the one-on-one talks that the communist regime is demanding.

The regime's impatience came days after its No 2 nuclear negotiator Ri Gun came away from meetings with Washington envoy Sung Kim without an agreement to hold bilateral talks.

"If the US is not ready to sit at a negotiating table with the (North), it will go its own way," the North's Foreign Ministry said Monday in a statement carried by Pyongyang's official Korean Central News Agency.

The statement did not elaborate, but it was widely seen as a warning that the North will bolster its nuclear stockpile - a brinksmanship tactic that the communist nation has often employed.

In Washington, State Department spokesman Ian Kelly did not comment on the North's statement, though he told reporters Monday that Kim "had very useful discussions" with Ri.

He also said the US is "still considering" North Korea's invitation for Stephen Bosworth, the US special envoy on North Korea, to visit Pyongyang for talks.

In September, the North said it was "weaponizing" plutonium, a key ingredient for nuclear bombs, and that it had succeeded in uranium enrichment, which would give the regime a second way to make atomic bombs. That was also seen as a pressure tactic aimed at getting Washington to agree to one-on-one negotiations.

North Korea has mixed such threats with a series of conciliatory moves, such as releasing two detained American journalists, after months of raising tensions with nuclear and missile tests. The North has also quit the six-nation nuclear disarmament talks - which involve China, Japan, Russia, the US and the two Koreas.

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