With the summer deadline approaching and no major update from North Korea in sight on the fate of Japanese nationals it abducted decades ago, some of the victims' relatives are expressing their disappointment in Pyongyang's investigation.

Senior officials from Japan and North Korea held talks in Sweden last May, at which point Pyongyang agreed to launch a special investigation into the abductees' whereabouts, raising hopes among their family members that momentum would build for a breakthrough on the issue.

Shigeo Iizuka is the 76-year-old brother of abductee Yaeko Taguchi, who disappeared in 1978 at the age of 22 and whose fate remains unknown. He thought that while it might be difficult for all of the abductees to quickly return to Japan, the probe could serve as a "trigger" that would pave the way for their eventual return.