North Korea: Sanctions on Kim Jong Un by US are 'declaration of war'

North Korea has said US sanctions imposed on leader Kim Jong Un by the United States are a "declaration of war".

The move by the US was described as “the worst hostile act” against the country in a statement issued by Pyongyang's foreign ministry carried by the official Korean Central News Agency.

The US Treasury Department imposed the sanctions on the North Korean leader and 10 other senior officials on Wednesday. They are set to affect property and other assets within US jurisdiction.

It was the first time that North Korean officials have been blacklisted by the US over human rights violations.

Acting Undersecretary for Terrorism and Financial Intelligence Adam J Szubin said in a statement: "Under Kim Jong Un, North Korea continues to inflict intolerable cruelty and hardship on millions of its own people, including extrajudicial killings, forced labour, and torture.”

In an initial response to the sanctions Pyongyang urged Washington to withdraw them immediately and threatened to instantly cut off all diplomatic channels if they failed to do so.

A statement said: "The United States has dared to challenge the highest authority of ours, committing the worst-ever hostile act that goes beyond confrontation over the so-called human rights issue. This constitutes an open declaration of a war.

"Now that the US has made a declaration of a war against us, all issues arising from relations with the US will forthwith be handled in accordance with DPRK's [the official acronym for North Korea] wartime laws."

Pyongyang will take "extremely strong countermeasures" in response, it added, but did not provide any more detail.

Speaking to reporters on a visit to the Ukraine on Thursday, Secretary of State John Kerry said North Korean officials at all levels needed to "consider the implications" of their actions.

He added that he spoke to his Chinese counterpart on Wednesday and reiterated the importance of China's help in pressuring Kim over his nuclear weapons program.

Earlier this year, Congress passed a new law requiring US President Barack Obama to deliver a report within 120 days on human rights in North Korea.

It designated sanctions for anyone found responsible for human rights violations. Kim Jong Un, the third generation of his family to rule the Stalinist state, topped the list.

Inside North Korea, however, Kim is considered infallible and a 2014 report by the United Nations, which referred to him by name in connection to human rights, triggered a strong reaction from Pyongyang, including a string of military provocations.

Additional reporting by agencies