SEOUL—North Korean leader Kim Jong Un hosted a high-level political delegation from the South for dinner Monday in Pyongyang and accelerated preparations for an inter-Korean summit during his first known meeting with officials from the rival government in Seoul.

The banquet, which stretched on for more than four hours, according to the South Korean president’s office, could signal a new phase of rapprochement as the two Koreas seek to expand a diplomatic thaw that started ahead of the Winter Olympics and saw North Koreans...