SEOUL (Reuters) - North Korea said on Friday that it was in the final stage of enriching uranium, a process that would give it a second path to making a nuclear weapon.
After a series of conciliatory gestures by the North over the past month, the announcement raises the stakes in efforts by the international community to convince the reclusive state to give up its nuclear weapons programme.
"Experimental uranium enrichment has successfully been conducted to enter into completion phase," the KCNA news agency quoted North Korea's United Nations delegation as saying in a letter to the head of the U.N. Security Council (UNSC).
The North has already tested two plutonium-based nuclear devices, the one in May triggering tightened international sanctions.
The Unites States has long suspected that the North has a secret programme to enrich uranium for weapons. Experts have said it has not developed anything near a full scale enrichment programme.
The North said its latest moves were in response to tighter sanctions.
"We are prepared for both dialogue and sanctions. If some permanent members of the UNSC wish to put sanctions first before dialogue, we would respond with bolstering our nuclear deterrence first before we meet them in a dialogue."
It added that reprocessing of spent nuclear fuel rods was at its final phase and extracted plutonium was being weaponised.
Pyongyang laid the blame squarely on the U.N. Security Council for sanctioning its rocket launch in April and ignoring one by South Korea late last month.
"Had the UNSC, from the very beginning, not made an issue of the DPRK's (North Korea's) peaceful satellite launch in the same way as it kept silent over the satellite launch conducted by South Korea on August 25, 2009, it would not have compelled the DPRK to take strong counteraction such as its 2nd nuclear test.
Pyongyang said its launch was to put a communications satellite into space. Others said it was to test a ballistic missile with the potential to hit U.S. territory.
It reiterated its opposition to six-nation talks over its nuclear weapons programme which it walked away from last December.
"We have never objected to the denuclearisation of the Korean Peninsula and of the world itself. What we objected to is the structure of the six-way talks which had been used to violate outrageously the DPRK's sovereignty and its right to peaceful development."
Those talks included the two Koreas, China, Russia, Japan and the United States and offered Pyongyang massive aid and an end to isolation if it gives up its efforts to build an atomic arsenal.
"If the UNSC only continues this standoff without making a proper judgement of which path is more favourable for the denuclearisation of the Korean Peninsula and of the world, the DPRK will be left with no choice but to take yet stronger self-defensive countermeasures as it had already warned," the letter said.
(Additional reporting by Yoo Choonsik, Cho Meeyoung and Jon Herskovitz)