Given the difficulty of solving all problems within a week, it is necessary to set up working groups "relatively separate within the mechanism of six-party talks", said Noriyuki Shikata during an exclusive interview with Xinhua.

The second phase of the fifth round of six-party talks also involve China, the Democratic People Republic Korea (DPRK), the United States, the Republic of Korea and Russia.

The talks in this phase are going on without "substantial progress" yet, Shikata said.

The spokesman noted that great differences still exist among the parties concerned, especially a wide gap between the DPRK and other parties.

"Japan still takes the six-party talks as an effective mechanism, and all parties agree it is the best way to cope with the nuclear issue within the framework." Shikata told Xinhua.

According to the spokesman, Japanese chief negotiator Kenichiro Sasae had met with Japanese Prime Minister Shinzo Abe and Foreign Minister Taro Aso before heading to Beijing for the nuclear talks.

They discussed Japanese stances and principles, and mentioned the nuclear, missile and abduction issues as the Japanese government's top concerns, hoping the current talks could have "a crucial step" toward the solution to those issues, Shikata said.

During the ongoing talks, chief nuclear negotiators from the DPRK and the United States on Tuesday held their first one-on-one discussions.

"The Japanese side has no plan yet for a bilateral meeting with the DPRK," Shikata said, adding Japan's dialogue with the DPRK is always open.

As to the duration of the current talks, Shikata noted it would be "open-ended" and depend on the progress made.