Mike Pompeo (L) shakes hands with North Korean leader Kim Jong Un in this undated image in Pyongyang, North Korea.

A meeting between U.S. Secretary of State Mike Pompeo and North Korean officials set for Thursday in New York has been postponed and will be rescheduled "when our respective schedules permit," the U.S. State Department said on Wednesday.

In a statement, it added, "Ongoing conversations continue to take place," but did not elaborate.

"The United States remains focused on fulfilling the commitments agreed to by President Trump and Chairman Kim at the Singapore summit in June," it said.

The exact reason for the postponement was unclear.

Pompeo had been due to hold talks with senior North Korean official Kim Yong Chol, which were hoped to have opened the way for a second summit of the two countries' leaders and make progress on denuclearization.

The meeting agenda had been to "discuss making progress on all four pillars of the Singapore Summit joint statement, including achieving the final, fully verified denuclearization" of North Korea, the State Department had said this week.

The June meeting of President Donald Trump and Kim Jong Un in Singapore was the first summit meeting of an incumbent U.S. president and a North Korean leader.

At that meeting, Kim Jong Un, who seeks relief from tough U.S.-led sanctions, committed to work toward denuclearization, but his steps since have fallen short of U.S. demands for irreversible moves to abandon a weapons program that potentially threatens the United States.