A trip to a Russian-held island off Hokkaido involving Japanese tourists on Russian visas raised eyebrows in the government Tuesday, with Chief Cabinet Secretary Yoshito Sengoku expressing concern the trip runs counter to Japan's territorial claim.

"It would be extremely disappointing," Sengoku told a news conference, adding the government was trying to verify details of the Monday visit.

The trip to Kunashiri Island was organized by a travel agency in the city of Fukuoka. It involved eight tourists aged 72 to 84 from Tokyo and Chiba, Kanagawa, Toyama, Osaka and Hyogo prefectures, as well as an attendant from the company. The trip is believed to be the first of its kind.