The meeting between Pompeo and Kim Yong Chol, the former spy chief and now top nuclear negotiator, "will now take place at a later date. when our respective schedules permit", the USA side said just after midnight on Wednesday, hours before Pompeo was supposed to travel to NY.
Ryder added that the Pentagon has already taken measures "to support Secretary Pompeo's efforts" like suspending large-scale joint drills with South Korea earlier this year.
At the State Department on Wednesday, deputy spokesperson Robert Palladino said the postponement "is purely a scheduling issue".
Koh Yu-hwan, a North Korea expert at Seoul's Dongguk University and a policy adviser to South Korean President Moon Jae-in, said a high-level meeting between the US and North Korea immediately after the USA midterm elections was never realistic, especially when the North was in no mood to make any concrete concessions.
To that end, the US and South Korea announced last week the creation of a new working group to "strengthen our close coordination", including on "sanctions implementation and inter-Korean cooperation that comply with the United Nations sanctions", according to State Department deputy spokesperson Robert Palladino.
"There have been cases in the past when US-North Korea talks were delayed, so there is no need to shift between hope and fear", a senior ministry official told reporters. "Some time next year, I would say".
Kim pledged to work toward denuclearization at an unprecedented first meeting with Trump in Singapore but negotiations have made little headway since, with North Korea falling short of USA demands for irreversible moves to abandon a weapons program that potentially threatens the United States.
Instead of following through on that, in recent days North Korea has been criticizing the USA over its sanctions, threatening last Friday to bring back its "byongjin" policy - advancing its nuclear arsenal and economic development at the same time. Seoul is of the view that Pyongyang can be encouraged towards nuclear disarmament through economic development, while Washington has set a complete shutdown of its nuclear weapons programme as a prerequisite for the lifting of sanctions.
Pompeo has traveled four times this year to North Korea, for decades a United States pariah, in hopes of securing an accord.
At the news conference, Trump pointed out that North Korea has not tested further missiles amid the talks.
U.S. and foreign sources close to the talks paint a picture that's starkly different from the image President Donald Trump sought to convey Wednesday, when he told reporters the administration is "very happy with how it's going with North Korea".
Pompeo has travelled four times this year to North Korea to work on achieving an accord.
The U.S. on Wednesday denied that it plans to reduce its military presence in South Korea after remarks from its top military officer sent alarm bells ringing.