North Korea's apparent preparation to test a long-range ballistic missile is merely a ploy to bring Washington back to the negotiating table, a leading expert on the Korean Peninsula said Wednesday in Tokyo.

"The greatest fear for North Korea is to be ignored by the U.S. Testing a Taepodong-2 is an attempt to demonstrate what it will do in such a case," said Masao Okonogi, a professor of political science at Keio University.

Just days after telling South Korea that it would annul past peacemaking agreements, media reported Tuesday that Pyongyang began preparing to test its long-range ballistic missile, which reportedly has a range of 4,300 km to 6,000 km.

Restarting negotiations with the United States is the prime concern for Pyongyang, and "everything else is subordinate to that," said Okonogi, suggesting South Korea's hardline policies toward the North had little bearing on the latest developments.

Talks on North Korea's denuclearization remain at a stalemate, but the expert asserted that the hermit state is unlikely to have developed the technology to mount a nuclear warhead on a long-range ballistic missile.

The focus will be on how the new U.S. administration reacts to the gesture, as President Barack Obama tries to work out how to handle diplomacy with the North while dealing with the ongoing financial turmoil and multiple other global challenges.

"The U.S. will probably not take an independent approach and (instead) harmonize with other allies (on) how to face North Korea," Okonogi said.