TOKYO - JAPAN'S parliament on Friday passed a law asserting sovereignty over four islands at the centre of a dispute with Russia, adding to tensions as the countries' leaders prepare to meet.

A law calling the four Kuril islands an 'integral part' of Japan was unanimously passed by the opposition-controlled upper house after the lower house also approved it in May when the bill sparked a protest from Moscow.

The four islets north of Japan's Hokkaido island - called the Southern Kurils by Russia and the Northern Territories by Japan - have been controlled by Moscow since they were seized by Soviet troops in 1945.

The spat has prevented the two countries from signing a post-World War II peace treaty.

Japanese Prime Minister Taro Aso last month told parliament the islands were illegally occupied by Russia, and Moscow has condemned the lower house vote last month as 'inappropriate and unacceptable'.

The law's passage comes as Aso plans to hold talks with Russian President Dmitry Medvedev on the sidelines of a Group of Eight summit in Italy next week, their second meeting this year.

The law says Japan will 'make the utmost efforts to realise the early return of the islands, which are an integral part of our country'.

It also aims to promote visa-free exchange programmes between the island's Russian residents and their Japanese former inhabitants and their families.

No breakthroughs were achieved at Medvedev's last meeting with Aso or in talks Aso held with Russian Prime Minister Vladimir Putin last month. -- AFP