By Charles Scanlon BBC regional correspondent

Koizumi has championed a more assertive foreign policy for Japan

He is restating a claim to the islands, known in Japan as the Northern Territories and in Russia as the southern Kurils.

They were seized by Soviet troops in the final days of the World War II.

The dispute has long soured relations between Tokyo and Moscow. Russia has reacted angrily to Mr Koizumi's visit.

He was waved off by former residents of the islands as he boarded a coastguard patrol boat for his tour around the disputed territory.

He said he intended to resolve the dispute for the good of Japan and Russia.

The three islands and a cluster of outcrops are now inhabited by a small community of Russian fishermen and their families.

Mr Koizumi said the islands were Japan's inherent territories and no peace treaty would be signed until they were returned.

The dispute has prevented Tokyo and Moscow from ever signing a peace treaty.

The government hopes the visit will reinvigorate negotiations, but the Russian foreign ministry said it would complicate efforts to resolve the dispute.

Mr Koizumi is one of the most nationalistic of recent Japanese prime ministers and has championed a more assertive role on the world stage.