SEOUL: An enraged North Korea responded to new UN sanctions with fresh threats of nuclear war Friday, vowing to scrap peace pacts with South Korea as it upped the ante yet again after its recent atomic test.

Pyongyang is renowned for its bellicose rhetoric, but the tone has reached a frenzied pitch in recent days, fuelling concerns of a border clash with both North and South planning major military exercises next week.

It has even threatened a “pre-emptive nuclear attack” against the United States and South Korea -- a notion dismissed as bluster by analysts, but not without dangerous, underlying intent.

North Korea “abrogates all agreements on non-aggression reached between the North and the South”, the state-run Committee for the Peaceful Reunification of Korea (CPRK) said Friday.

The CPRK said the pacts would be voided as of Monday, the same day that Pyongyang has vowed to rip up the 1953 armistice agreement that ended Korean War hostilities.

It also announced the immediate severing of a North-South hotline installed in 1971.

State television, meanwhile, showed North Korean leader Kim Jong-Un laying preparations for “all-out war” as he visited a frontline military unit involved in the shelling of a South Korean island in 2010.

The November shelling came eight months after the sinking of a South Korean naval vessel with the loss of 46 lives that was also blamed on Pyongyang.

While North Korea is not deemed capable of any nuclear strike on the US mainland, there are growing fears that it will mount some provocation in the form of a missile test or a similar artillery assault.

“To me, this feels like the most dangerous situation since the Korean War,” said Paik Hak-Soon, a North Korean analyst at the Sejong Institute in Seoul.

“The North is cornered more than ever in the international community and will keep pushing ahead with even more confrontational moves militarily,” Paik told AFP.

South Korea's new president, Park Geun-Hye, who was sworn in less than two weeks ago, said the situation had become “very grave” but vowed to “deal strongly” with any provocation from the North.

The CPRK statement came hours after the UN Security Council beefed up existing sanctions on the communist state in response to its February 12 nuclear test.

The resolution adopted by the 15-member Council tightened restrictions on North Korea's financial dealings, notably its suspect “bulk cash” transfers.

The new sanctions will “bite hard”, said the US ambassador to the UN, Susan Rice. “They increase North Korea's isolation and raise the cost to North Korea's leaders of defying the international community.” China wants “full implementation” of the resolution, said its UN envoy Li Baodong, while stressing that efforts must be made to bring North Korea back to negotiations.

In Beijing, foreign ministry spokeswoman Hua Chunying urged “relevant parties to exercise calm and restraint, and avoid actions that might further escalate tensions,” describing the situation as “highly complex and sensitive”.

Prior to the Security Council meeting, the North Korean foreign ministry had threatened a “pre-emptive nuclear attack” against the United States and all other “aggressors”.

The United States responded by saying it was “fully capable” of defending itself and its allies -- including South Korea -- against any missile strike.

Friday's CPRK statement condemned the UN resolution as proof that Washington and its “puppets” in Seoul were “hell bent” on confrontation.

“North-South relations have gone so far beyond the danger line that they are no longer reparable and an extremely dangerous situation is prevailing...where a nuclear war may break out right now,” it said.

An annual US-South Korea military exercise known as Foal Eagle is currently under way and another joint drill is scheduled to begin Monday.

The North is believed to be gearing up for nationwide military manoeuvres of its own next week, involving the three main wings of its armed forces.

In such a volatile atmosphere, “there's always that risk of a miscalculation and rapid escalation”, warned Dan Pinkston, a Seoul-based security expert for the International Crisis Group.

“Most of this is bluster, but the regime in North Korea is also signalling that it's willing to take greater risks, and that's a dangerous sign,” Pinkston told AFP.