Parties to the six-way talks have held preliminary meetings in Beijing ahead of the fourth round of the discussions on North Korea's nuclear program.

South Korean officials led by Deputy Foreign Minister Song Min-soon on Sunday will hold talks with top delegates from North Korea and China. Pyongyang and Beijing also held a bilateral meeting.

Seoul will explain its proposed role as mediator between Pyongyang and Washington.

The six parties will also discuss achieving substantial progress in this round.

Washington will hold bilateral meetings with Seoul, Pyongyang and China before the talks formally begin Tuesday.

Delegations from the United States, Japan and Russia are to arrive Sunday.