SEOUL, Feb. 9 (Xinhua) -- Stephen Biegun, U.S. special representative for the Democratic People's Republic of Korea (DPRK) affairs, said on Saturday that talks in Pyongyang with the DPRK side were productive.

Biegun made the remarks during his meeting in Seoul with South Korean Foreign Minister Kang Kyung-wha, saying the DPRK and the United States have been making efforts for a substantial progress though issues remained to be tackled.

The U.S. envoy visited the DPRK for three days through Friday ahead of the planned second summit in Vietnam in late February between top DPRK leader Kim Jong Un and U.S. President Donald Trump.

Biegun explained the outcome of his Pyongyang visit to Kang, Seoul's foreign ministry said in a statement without elaborating further.