During his surprise visit to Pyongyang, Isao Iijima, a special advisor to Prime Minister Shinzo Abe, explained to officials there that Tokyo continues to seek "comprehensive solutions" to the North's abductions of Japanese and to its nuclear arms and missile threats, a source said Saturday.

Iijima, who returned to Tokyo via Beijing the same day, stressed to Pyongyang that the return of Japanese abducted by North Korean agents in the 1970s and 1980s is a major goal and if no progress is made toward this end, Tokyo will not proceed with talks, the source said.

South Korea and the U.S. are concerned, however, that Iijima's unannounced trip may signal Japan might ease its pressure on the hermit state in exchange for concessions on the abduction issue. Seoul, Tokyo and Washington had been pressing the North to drop its nuclear and missile threats.

Iijima met Chief Cabinet Secretary Yoshihide Suga at a Tokyo hotel for about one hour to report on his visit to Pyongyang. Suga later declined to give any comments, citing the sensitive nature of Iijima's talks with senior North Korean officials.