The abduction issue has long been a major obstacle in the frosty ties between the two nations, which have no formal diplomatic relations.

The Japanese delegation, led by Junichi Ihara, head of the Asia and Oceania affairs bureau at Japan's Ministry of Foreign Affairs, is to stay in North Korea for four days.

After years of denial, North Korea acknowledged in an unprecedented 2002 summit between Kim Jong Il and then- Prime Minister Junichiro Koizumi that its agents had kidnapped 13 Japanese, mainly to train spies in Japanese language and culture. It allowed five of them to return to Japan that year, but said the others had died.

Japan believes hundreds more may have been abducted and some may still be alive.

In what was seen as a significant breakthrough after years of stalemate, North Korea agreed in May to launch a new probe into the abductions. In exchange, Japan agreed to ease some unilateral sanctions on North Korea, though it continues to enforce sanctions backed by the United Nations over North Korea's nuclear and long-range missile programs.

But progress in North Korea's re-investigation has been slower than Tokyo had hoped.

In September, Ihara and his North Korean counterpart, Song Il Ho, held a meeting in the northeastern Chinese city of Shenyang. Japan was hoping then to receive a preliminary report on the investigation, but none was presented.

Japanese Prime Minister Shinzo Abe said the delegation is being sent to convey that the resolution of the issue is a high priority for Japan. He has promised not to relent until all of the abductees are returned to Japan or accounted for.

That could prove to be a very complicated and sensitive matter since estimates of the number of abductees range from the 17 that the Japanese government officially acknowledges to more than 800 that Japanese police list as cases of missing persons in which abductions by North Korea cannot be ruled out.

The last time the two sides had talks in Pyongyang was in November 2004, six months after Koizumi's second visit.