United States Special Representative for North Korea Stephen Biegun reportedly said that "he doesn't know" when asked about reports that a senior North Korean official involved in Pyongyang's nuclear negotiations with Washington had been executed.

CNN reported on Saturday Biegun's response to questions about media reports that the North's special envoy to the U.S. Kim Hyok-chol has been executed over the failure of the February summit between North Korean leader Kim Jong-un and U.S. President Donald Trump.

Biegun, who is visiting Singapore to attend the annual Asia Security Summit, also known as the Shangri-La Dialogue, reportedly quoted U.S. Secretary of State Mike Pompeo as saying that the U.S. is attempting to check the reports.

The White House on Friday refused to comment, just saying it is monitoring the situation, while Pompeo said the same state that Washington is doing its best to validate the reports.

Kim Hyok-chol was Biegun's counterpart for the working-level talks ahead of the second U.S.-North Korea summit in Hanoi.