New Delhi, Aug. 13 -- Russian President Vladimir Putin's visit to the disputed Kuril Islands has triggered a strong reaction from Japan, adding another strain to already tense relations between Tokyo and Moscow.

Putin visited Iturup, one of the southern Kuril Islands, on Thursday (August 13). Japan claims the island, which it calls Etorofu, as part of its Northern Territories. Tokyo described the visit as "absolutely unacceptable" and formally protested to Russia.

Putin's trip was his first visit to the Kuril Islands as Russian president. He toured a fish-processing plant, a hospital and a school on Iturup, met local residents and held talks with Sakhalin Governor Valery Limarenko.

The visit came after Putin travelled to nearby Sakhali...