In the latest in a spate of increasingly threatening warnings by North Korea, the country's Foreign Ministry has urged the U.S. to "change its current method of calculation" in nuclear negotiations or risk turning last year's Singapore joint declaration into a "mere blank sheet of paper."

The statement by an unnamed ministry official carried by the official Korean Central News Agency (KCNA) late Tuesday said the fate of the declaration that emerged from last June's historic Singapore summit between U.S. President Donald Trump and North Korean leader Kim Jong Un "will not be promising" if the United States "fails to carry out its obligation" and continues its "hostile policy" toward the country.

"It is regrettable to see that the United States has become ever more undisguised during the past year in its scheme to annihilate us by force while deliberately turning its face away from the implementation of the DPRK-U.S. Joint Statement and only insisting on our unilateral surrender of nuclear weapons," the statement said, using the acronym for the North's formal name, the Democratic People's Republic of Korea.