North Korea threatened neighbouring South Korea with their "final destruction" during a UN Conference on Disarmament, a week after it conducted its third nuclear tests.

The secretive communist state also warned that could also take "second and third steps" in its nuclear programme following the underground test on 12 February.

North Korean diplomat Jon Yong-ryong told the UN: "As the saying goes, a new-born puppy knows no fear of a tiger. South Korea's erratic behavior would only herald its final destruction."

The diplomat also stressed that Pyongyang had recently taken a "resolute step for self-defence" that Jon described as "strong counter-actions to a foreign aggressor," Reuters reported.

Without directly referring to the country's recent nuclear testing, Jon added: "If the US takes a hostile approach toward the DPRK to the last, rendering the situation complicated, it [North Korea] will be left with no option but to take the second and third stronger steps in succession."

The comments were quickly condemned by ambassadors from other countries at the meeting on disarmament.

US Disarmament Ambassador Laura Kennedy criticised the language of the statement and how it was in direct contradiction to the "goals and objectives" of the conference.

She said: "I also was particularly struck by the phrase 'heralding the destruction of the Republic of Korea' and find that language incredibly inconsistent with the goals and objectives that this body is intended to pursue."

The Ambassador for Britain, Joanna Adamson, described the comments from North Korea as "completely inappropriate", adding: "It cannot be allowed that we have expressions which refer to the possible destruction of UN member states."

North Korea had previously told its ally China that it is preparing one or two more nuclear tests this year in what is considered an effort to force diplomatic discussions with the US.

A senior source who has "direct knowledge" of the matter told Reuters: "It's all ready. A fourth and fifth nuclear test and a rocket launch could be conducted soon, possibly this year."