Seoul (AFP) - North Korea said Friday that the new US sanctions targeting its leader Kim Jong-Un amounted to a "declaration of a war" and vowed to take strong retaliatory measures.

The move by the United States constituted "the worst hostility" against the North, Pyongyang's foreign ministry said in a statement, carried by the official Korean Central News Agency.

Washington on Wednesday placed Kim on its sanctions blacklist, calling him directly responsible for a long list of serious human rights abuses.

The sanctions are the first that name the country's "Supreme Leader", as well as the first targeting the reclusive state for rights violations.

In its first reaction to the move, Pyongyang urged Washington to retract the sanctions immediately, warning that the North would instantly cut off "every lever and channel for diplomatic contact" between the two countries if the US failed to do so.

"The US dared challenge the dignity of the DPRK supreme leadership, an act reminiscent of a new-born puppy knowing no fear of a tiger," the statement said, using the official acronym for North Korea.

"This is the worst hostility and an open declaration of war against the DPRK as it has gone far beyond the confrontation over the 'human rights issue'."

"Now that the US declared a war on the DPRK, any problem arising in the relations with the US will be handled under the latter's wartime law," it said.

Strongly worded retaliation by Pyongyang is not unusual, and it has previously described actions by the US and neighbouring South Korea as declarations of war.

But the reference to "wartime law" is rare, and suggests Pyongyang will officially treat the US as if they are engaged in a conflict.

The statement said the reclusive nation will take "the toughest countermeasures to resolutely shatter the hostility of the US", but did not elaborating on what this could entail.

- Personal insult -

Ten other top Pyongyang officials were also blacklisted by the US on Wednesday, accused of being behind widespread abuses that have made North Korea "among the world's most repressive countries".

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South Korea on welcomed the move by the US, saying it hoped it would shine a light on human rights "violations" in the North.

South Korean analysts had anticipated that the North would react angrily to what they would likely perceive as a "personal insult" against Kim.

Kim, who took power four and a half years ago after the death of his father Kim Jong-Il, is the subject of a personality cult that permeates every aspect of life in the repressive state.

"There will be a bombardment of diatribes from North Korea against the US as the military, government agencies and various social groups are likely to fall over themselves to prove their loyalty to Kim", Professor Yang Moo-Jin of the University of North Korean Studies told AFP.

But, he said, the North would probably wait until the start of the annual joint US-South Korea military exercises that begin in August to flex its military muscle.

Professor Kim Yong-Hyun of Dongguk University said the North would ratchet up tension but it would stop short of conducting another nuclear test to avoid further alienating its main ally and economic benefactor China.

The international community has issued to a series of increasingly harsh sanctions on North Korea this year linked to its nuclear programme.

Pyongyang conducted its fourth nuclear test in January and a missile test, disguised as a satellite launch, in the following month.