South Korea and Japan are also suspicious of calls to restart the six-nation talks. The other two parties to the talks, Russia and China, have been more supportive of getting the dialogue back on track.
In his speech to the forum, Chinese Foreign Minister Wang Yi said the parties should seize on a warming trend on the Korean Peninsula to take whatever actions are needed to restart talks.
"The situation on the peninsula was relatively stable when each party actively participated in negotiations. The situation was tense or even directionless when the talks stalemated," Wang said.
Since the breakdown in talks, Pyongyang has ramped up tensions with a third nuclear test and a long-range rocket launch, prompting a tightening of U.N. sanctions against the isolated communist regime. Recent months have seen the North take a more moderate line as it sought to restart contacts with Seoul and repair ties with China, its most important ally.
The 10th anniversary forum had been promoted as a way of highlighting the achievements of the negotiations, but there were no immediate signs that it had brought the sides any closer.
The U.S. Embassy in Beijing said that it was sending a diplomat to attend only as an observer and that there were no plans to meet with any North Korean representatives.
Washington is focused on building consensus among the other six-party nations to increase pressure on Pyongyang.
U.S. Secretary of State John Kerry is due to meet his Chinese counterpart Wang in Washington on Thursday, and North Korea's nuclear program will be a key part of their discussions, Harf said.