U.S. Assistant Secretary of State James Kelly and Mitoji Yabunaka, a senior official at the Foreign Ministry, held an "intensive discussion" Monday in Tokyo focusing on how North Korea may be given security assurances.

The talks form part of preparations ahead of a second round of six-way talks centering on Pyongyang's nuclear arms program.

Earlier in the day, Kelly held separate meetings with Chief Cabinet Secretary Yasuo Fukuda and Shinzo Abe, secretary general of the Liberal Democratic Party.

Kelly and Abe agreed to take up the abductions issue during the next round of six-way talks, which are expected to be held in mid-December.

"We reviewed our efforts to help prepare for the next round of six-party talks so that we can carefully work our positions to have the best opportunity for a successful round," Kelly told reporters after his meeting with Fukuda.

Kelly and Yabunaka talked about providing North Korea with security assurances on the basis of a proposal drafted by the U.S., as well as about steps Pyongyang should take if and when it agrees to abandon its nuclear program, according to a Foreign Ministry official.

Though both sides refused to unveil the details of their talks, a Japanese official said that Japan and the U.S. are still divided over the contents of the document regarding North Korean security concerns.

While the U.S. is willing to spell out that "the U.S. will not invade" North Korea in a written statement, the Japanese side is reluctant to do so, according to the official.

U.S. President George W. Bush has repeatedly stated that Washington has no intention of invading the North and it would not be necessary to repeat this pledge, the official added.

Kelly will meet with Foreign Minister Yoriko Kawaguchi before heading off to China on Tuesday. He will also visit South Korea before returning to Washington.