A Japanese researcher and pundit on the economies and cultures of both North and South Korea was detained near the border between China and North Korea by Chinese authorities for half a day this week, he said after returning to Japan on Wednesday.

Toshio Miyatsuka, a professor at Yamanashi Gakuin University, said Thursday he and his wife were detained early Tuesday while he was taking photos and video from Jian, Jilin Province, of a bridge over the Yalu River, which forms the border between China and North Korea there.

The security authorities alleged the couple trespassed into a military-controlled area and fined them 500 yuan (about ¥6,000) each, Miyatsuka said..

"I visited the same place in March and there were no signs saying it was a military-controlled area. It was a ridiculous investigation," said Miyatsuka, who entered China on Sunday.

Miyatsuka has written several books on the daily culture and economic activities of people in North and South Korea, and comments on Korean affairs on TV programs and in other major news organizations' reports.