The United States' top nuclear envoy Christopher Hill has called his recent nuclear discussions with North Korea very substantive.

He briefed his South Korean counterpart Kim Sook about the results of the Pyongyang talks in Seoul. But he declined to elaborate on the details of the discussions in a meeting with reporters.

Hill said that his main dialogue partner in the latest discussions was North Korean Vice Foreign Minister Kim Kye-gwan. He said that he also met with North Korean Foreign Minister Pak Ui-chun and North Korean military figures including a North Korean representative at the border truce village of Panmunjeom.

It’s the first time for Hill to meet with North Korean military officials during a visit to the North. He has made three visits to the communist country.

Hill arrived in Pyongyang on Wednesday and planned to return to Seoul the next day. But he extended his stay by one more day for additional discussions with the North.

The U.S. top nuclear envoy left for China Saturday morning for meetings with Chinese Vice Foreign Minister Wu Dawei and the Russian ambassador to Beijing. He will head home to the U.S. on Saturday night.