GENEVA (Reuters) - The United Nations’ top human rights body agreed on Friday to widen its investigation into widespread violations in North Korea with a view to documenting alleged crimes against humanity for future prosecution.

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North Korea said it “categorically and totally” rejected the resolution adopted by the U.N. Human Rights Council. The text was “a product of the U.S. hostile policy toward the DPRK (Democratic People’s Republic of Korea) from A to Z,” its envoy said after boycotting the debate.

The 47-member state forum adopted a resolution, brought by Japan and the European Union and backed by the United States, on the final day of its four-week session without a vote. It called for North Korea to cooperate and allow access for U.N. investigators, which the reclusive state has never done.

International pressure is building on the country ruled by Kim Jong Un over its nuclear tests - Fox news reported on Thursday North Korea was in the final stages of launching another one, possibly within days.

The United States has imposed fresh sanctions on foreign companies or individuals for violating export controls on North Korea, as well as Iran and Syria, the State Department said on Friday.

The U.N. human rights office in Seoul would be strengthened for two years with international criminal justice experts to establish a central repository for testimony and evidence “with a view to developing possible strategies to be used in any future accountability process”.

The Seoul office’s current six-strong staff record testimony from interviews with dozens of North Korean defectors each week, a U.N. official told Reuters.

“This not only brings North Koreans one step closer to justice for human rights crimes they have suffered, but should also make North Korean government officials think twice before inflicting more abuse,” John Fisher from Human Rights Watch said in a statement.

A U.N. commission of inquiry, in a landmark 2014 report based on interviews and hearings with defectors, cataloged massive violations - including large prison camps, starvation and executions - that it said should be brought to the International Criminal Court.

“The ‘resolution’ is nothing more than a document for interference in internal affairs of sovereign states and represents the culmination of politicization, selectivity and double standards of human rights,” Mun Jong Chol, a counselor at North Korea’s mission to the U.N. in Geneva, told reporters.

It was a fraudulent document full of “lies, fabrications and plots”, Mun said.

China said it “dissociated” itself from the council’s decision and called for dialogue.

The situation on the divided Korean peninsula is “complex and sensitive” and all sides should avoid provocation that might lead to an escalation, Chinese diplomat Jiang Yingfeng said.

The world should “focus on the bigger picture,” he added.