Yongbyon nuclear scientific research center in North Korea (Photo: AFP/VNA)

In a speech in Palo Alto, California, Biegun said Washington will have to have expert access and monitoring mechanisms for key nuclear and missile sites to ensure removal or destruction of stockpiles of fissile material, weapons, missiles, launchers, and other weapons of mass destruction.

The same day, the US State Department announced that Biegun will travel to Seoul on Sunday and later meet with his North Korean counterpart Kim Hyok-chol in Panmunjom.