On Saturday, the Russian premier landed on Iturup - one of the four islands forming the Kuril archipelago that lie off Russia's far-eastern coast and Japan's north. Medvedev was to inspect some infrastructure projects and attend a youth forum on the island, Russian media reported.
"Everything is perfectly modern here," the Russian prime minister was quoted as saying upon his arrival. "This is the result of our development program for the Kuril islands," he added.
But the Japanese government reacted strongly to Medvedev's visit. Hajime Hayashi, the head of the Japanese foreign ministry's European division, phoned the Russian ambassador in Tokyo to lodge a formal protest.
"The trip contradicts Japan's position over the Northern Territories and hurts the feelings of the Japanese people… It is extremely regrettable," Hayashi said.
According to Medvedev's Instagram account, the premier took selfies with the participants of a government-led youth forum in front of a big Russian flag to mark Russia's flag day.
"At the Kurils on Russia's State Flag Day," read the caption of a picture.
In 2014, Russia's military drills on the islands, which are known as the Northern Territories in Japan, were slammed by Tokyo. Medvedev, then president, also visited the archipelago in 2010.
The dispute over the Kuril islands has long strained the ties between Japan and Russia, preventing the two countries from signing a post-war peace treaty.
shs/ng (dpa, AFP)