U.S. President Donald Trump failed to fulfill a promise made to North Korean leader Kim Jong-un during their historic June summit in Singapore that he would soon sign a declaration ending the Korean War, according to a report published Wednesday.

Vox News highlighted how Trump's decision to ‘move the goalposts and make it conditional’ led to the recent stalemate in negotiations between Washington and Pyongyang.

The report said Trump had promised to sign the peace declaration, which would officially put an end to the war between North and South Korea, but months have passed and nothing has happened.

The Trump administration is now saying that North Korea needs to get rid of its nuclear arsenal first before it can sign any peace agreement, while Pyongyang is saying Trump's failure to keep his word has made it reluctant to denuclearize.

"I’m not familiar with that being part of the overall agreement, but I can tell you that we believe that denuclearization has to take place before we get to other parts," State Department spokeswoman Heather Nauert said in response to a question from a reporter.

The White House has yet to make any statements on the issue.

Trump and Kim met on June 12 in Singapore and reached an agreement on the removal of nuclear weapons in North Korea.

But the diplomatic harmony between the two countries deteriorated in the ensuing weeks, and the U.S. began accusing Pyongyang of not making any progress on dismantling its arsenal.

While fighting between the two Koreas was paused with the July 1953 armistice, the war has technically continued because no formal peace treaty has been signed.