Confusion is spreading after teaching materials on the Japanese language brought in by four lecturers sent from Japan to one of four Russian-controlled islands as part of visa-free exchange activities were seized by Russian customs authorities.

The lecturers arrived on the island, called Kunashiri in Japanese, on June 15, planning to stay there until late July to hold Japanese language classes for Russians.

They may return home earlier than scheduled as it is difficult to give lessons without the teaching materials, sources said.

Russia's Interfax news agency reported Friday that the teachers may leave Kunashiri on Monday.

The four islands, located off Hokkaido, were seized by the former Soviet Union from Japan at the end of World War II.