Hill also said that the DPRK needed to do more to address its relationship with Japan.
A Japan-DPRK meeting took place in Hanoi early March without achieving any breakthrough in resolving outstanding issues preventing the two countries from normalizing relations.
Japan's envoy Kenichiro Sasae said in the chief envoys' meeting that Japan would try to implement the initial steps quickly, adding that parties should start thinking about measures in the second stage.