President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE promised North Korean leader Kim Jong Un that he would sign a declaration ending the Korean War during their June summit in Singapore, according to a new Vox report.

Trump told Kim he would sign the peace declaration shortly after the meeting, sources familiar with the discussions told Vox. However, in the months since the summit, Trump has not done so, instead stating Pyongyang must denuclearize before he signs the agreement.

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One source said Trump's failure to sign the treaty in the months since the summit could partially explain North Korea's unwillingness to dismantle their nuclear arsenal.

“It makes sense why the North Koreans are angry,” the source told Vox. “Having Trump promise a peace declaration and then moving the goalposts and making it conditional would be seen as the U.S. reneging on its commitments.”

“We are committed to building a peace mechanism with the goal of replacing the Armistice agreement when North Korea has denuclearized," a State Department spokesman said in a statement to The Hill.

The White House declined to comment for Vox's story, and did not immediately respond to The Hill's request for comment.

The Korean War ended with an armistice after three years of fighting in 1953, meaning the war is not over by legal standards. The war still would not be over if the U.S. and North Korea signed a treaty because they would still lack China's signature.

National security adviser John Bolton and Secretary of Defense James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE have come out against the president signing a peace declaration, Vox reported.

North Korean officials on Tuesday warned in a letter that denuclearization talks are "again at stake and may fall apart," according to CNN.

Trump and Kim signed onto an agreement that promised the denuclearization of the Korean Peninsula without specifics as to how that would be achieved. The country has shown few signs that it intends to follow through on the promise, with the United Nations recently reporting there is no indication Pyongyang has stopped its nuclear activities since the summit.

The country has stated numerous times that the U.S. is not holding up its end of the bargain since the Singapore summit.