China says that South Korea's past nuclear activities, along with mistrust between North Korea and the United States, are complicating the process of the six-party talks on settling North Korea's nuclear standoff.

Chinese Foreign Ministry spokesman Kong Quan said at a regular news briefing Tuesday that there are quite a lot of difficulties in holding the six-nation talks as planned.

Kong hinted at the possibility of discussing South Korea's nuclear experiments at the six-party talks, calling it one of the many issues that must be dealt with to realize the denuclearization of the Korean Peninsula.

Kong's comments come after North Korea said last Thursday that it will not participate in the multilateral talks until an investigation is carried out into the recent revelations of South Korea's past nuclear activities.