When the talks come to details, such as how to dismantle the reactor, it will become harder to push forward the process, said Li Dunqiu, an expert on the Korean Peninsula issue with the Chinese Academy of Social Sciences.

As part of the energy assistance that the other five parties promised the DPRK at the fifth round of the six-party talks in February this year, 6,200 tons of heavy oil arrived at the Songbong port of the DPRK Saturday morning, followed by the DPRK's announcement of its closure of the Yongbyon nuke reactor.

Amid welcome to the long-awaited shutdown from other parties is the uncertainty about how the following talks will go along.

The Yongbyon reactor shutdown is doubtlessly the crux of the matter, but never the hardest process in the talks. Analysts believed the next stage will be more difficult, as the DPRK, according to former agreements, is required to declare all its nuclear programs and disable all existing nuclear facilities in the following stage.

"The following bargaining process will be much more complicated," Li said.

However, the DPRK's top negotiator Kim Kye Gwan conveyed an encouraging message Tuesday before leaving for Beijing, pledging that the DPRK will spare no efforts to make Wednesday's meeting a success.

"The first phase has been accomplished, and now it's time to take new actions. The talks will focus on the obligation and actions to be taken by the concerned parties in the second phase," he said.

There will be no opening ceremony for Wednesday's meeting. The top negotiators from China, the United States, Russia, the DPRK, the Republic of Korea (ROK) and Japan will directly go through the main agenda in a "down to earth" manner, including evaluating the implementation of the February joint document and discussing what to do in the next phase, according to an official of the Chinese Foreign Ministry.

Despite the anticipation of difficulties, the six-party talks has proved an effective platform for solving the Korean Peninsula nuclear issue, as demonstrated by the shutdown of the Yongbyon reactor after rounds of negotiations.

In addition to the nuclear crisis, the six-party talks have been extended to cover issues ranging from peace on the peninsula and the relations between the DPRK and the United States and Japan.

As all the parties are seeking a regional security cooperation mechanism, a working group of the northeast Asia peace and security mechanism has been initiated under the framework of the six-party talks.

"The talks may extend further and touch other agendas, which can help push forward the denuclearization process," said Shi Yinhong, an international relations professor with the Beijing-based Renmin University of China.