The U.S. and North Korea are set to hold high-level talks in NY on Thursday.
The talks between President Donald Trump's top diplomat and the North Korean delegation were due to be held on Thursday.
The State Department announced the decision to reschedule the meeting in the middle of the night as results from the USA midterm elections were coming in.
Secretary of State Mike Pompeo will meet with senior North Korean official Kim Yong Chol in NY on Thursday to discuss North Korea's denuclearization.
"Pompeo's meeting with officials from the Democratic People's Republic of Korea, scheduled for this week in NY, will now take place at a later date", Nauert said.
Nauert said the United States remained focussed on fulfilling the commitments agreed to by President Donald Trump and North Korean leader Kim Jong-un at the Singapore summit in June, reported The Washington Post.
South Korean presidential spokesman Kim Eui-kyeom said later Wednesday that his government doesn't believe U.S.
North Korea has been pushing for such a declaration before it takes any further steps toward denuclearization, but Washington fears that this would rob it of a powerful negotiating card.
"If denuclearization talks reach a final phase and North Korea begins to give up its nuclear weapons, they (North Korea) would want to bring up the issue of USFK and change its characteristics in accordance with a new security environment".
Seoul's Foreign Ministry also expressed hope that the USA and North Korea can quickly reschedule a high-level meeting. But the Blue House would not reveal the reason for the postponement and referred questions to the State Department.
The sources told CNN that North Korea, for its part, is looking for the United States to offer something before moving forward, but that the United States has not been willing to give anything up first, such as easing the punitive sanctions levied on the Kim regime. The North stopped short of threatening to abandon nuclear negotiations with Washington.
However, Ryder said the Pentagon "must be prepared to adjust as appropriate" if negotiations with North Korea advance, indicating that there could be changes to the military exercises with South Korea that are scheduled to take place next year.
Trump's engagement with North Korea in recent months was apparently timed to the midterms, but he will no longer agree to major meetings if there are no realistic expectations of progress in nuclear diplomacy, Koh said.